I am looking into about the same thing your are, a 25 x 30 with concrete .The concrete price is around 1000. thats if I do the labor myself. the structure is about 12000. and you put it together. It's like a quonset hut (military style, like gomer pyle). Looks like it goes together rather easy and fast and you don't need many people to put it up. They sell insulating panels for it, but I think that I could insulate it cheaper.
Although I have only seen something like this done once, I think it might work.
Start with a concrete slab and 2 shipping containers. Place the containers so many feet apart to make the size you need. Place pre-fab trusses over the resulting area, where the trusses create the whole roof structure and span the containers. Enclose the open areas; roof with steel.
My preference would be to have trusses made up for this specific purpose, but you might find off-the-shelf parts that would work.
You could insulate just the center section. Regardless, you would get an enclosed space quite quickly.
Not sure of the cost or how much of the work you can do yourself, but insulating concrete forms might fit the bill. They are like large Logo blocks that are hollow and filled with concrete. Some of the outfits that build these type of structures will let you do the form construction yourself. The local outfit will even send a rep on delivery day to show you how to do it.
My local building store (Minnesota/Wisconsin chain) sells pole barn plans/kits. Key in your specs to a kiosk display unit with things like length, width, overhang, sidewall height, number of service doors, number of sliding or overhead doors, windows, etc. and bingo: material list that you hand to the counter guy. Everything is delivered to your site a couple weeks later, all steel cut to length in your choice of a couple dozen colors. 1200 square foot with decent doors and a couple of windows runs about $5500. Or go bananas and do a 50'x90' with 16' walls for $22,000. (hint: $5 to $8 per square foot depending on size) You put it up. Only hassle with these is hoisting the roof trusses into place. Everything else is one or two guys plugging away at it. If you add the options like colored roof and walls, overhangs, some windows, they can look quite nice.
These are completely custom so you can have sidewalls of any reasonable height (8' to 14' is the usual range)
You need to insulate the roof (not included in the price) at the time you build it so it doesn't rain inside from the condesation. Sidewalls can be insulated or not, added later, or just insulate one section.
Typical setup in the cold climes is to build a fairly big building, do an insulated and heated smaller shop in one corner, store stuff in the rest of the building. You can even cheap out and put concrete in only the one section. Or add the concrete later when you have the $$
. A local company recently did a building where I work with these. It is very well insulated. It took their crew (mostly Amish) about two days to put the forms together on a 600 sq. ft. "L" shaped building. This included a flat concrete roof (you could do trusses). Again, I don't know how this compares to other options with respect to cost but if you want a well insulated and strong building, IMO this would be an option to consider. Hope this helps.
I got my building from these people you can spec out the building you want on their site and they will ship it to you complete except for the foundation bolts.
some times the above place has a building that some one put the deposit on and they built that they sell at a discount ( however that's not the best way to buy one as your local building codes are not likely to be the same.)
A metal building is normally one of the cheapest ways to get covered sq footage
My shop is built with foam and comcrete. The product is called Quad-Lock but there are other similar products. In essence, you build double walls with strofoam "Lego" blocks held apart by little plastic trays. The horizontal re-bar lies in the trays and the vertical goes down through them. You then fill the space between with concrete. The floor was then poured afterward. The result is a well insulated building with an enormous thermal mass. The 22,000 btu/h radiant heater is more than enough even in a Canadian winter and the shop is often 10 to 15 degrees C cooler then outside in a summer hot spell.
The roof was fairly conventional cathedral trusses, R-40 insulation and white (reduces radiation/absortion of heat) steel roofing.
Cost is a little more than conventional studs and particle board construction but not much.
I'm building my new workshop out of structural insulated panels... two 1/2" layers of cement bonded particleboard with 5" of PU foam bonded between them. According to the calculations I did, this will be cheaper than an insulated concrete building and should be at least as good if not better in terms of strength, sound and heat resistance.
I'm in the UK, but SIPs are more common in the States than here, so you may get better prices than I can.
The 30' x 40' garage I just built used Eco-Blocks for the knee wall. They are one of the ICFs (insul concrete forms) on the market and were really simply to put together. HOWEVER, I did only the knee wall (32" high, half was underground) instead of the entire wall because they are expensive. Plus, even though I tied them to the rebar beyond what the manufacturer said was necessary, they still moved a little when we started pumping a couple tons of concrete into them. One 40' wall has a 1/2 bow in it, not a big deal but it's annoying as hell after all the trouble I went through to get them straight during the tie down. Then you also have to consider that the foam needs to be covered so you have to pay for something (I used stucco coating) so they are not exposed.
After just getting the garage finished, we are now moving so I am planning Garage / Shop version 2. No ICFs in the plan. Just 2 x 6 walls although thinking about 2 x 8s.
Since money is an object I would suggest going into some local subdivisions and seeing how the contractors build them. There are good reasons ($$$$) why you don't normally see the newer, high tech building materials like ICFs, SIPs, Hebel blocks, etc being used. Then check on the metal buildings as they are really the only other decent option.