propane on acetylene torch?

It depends on the torch, but probably not. But if you can find cheap oxy-acetylene torches, you may well find an oxy-propane torch from the same source.
I use a BOC Saffire 5, which is an expensive torch body with a separate mixer that's relatively cheap. If I change the mixer, then I can use either acetylene or propane. It is _not_ safe to use the wrong mixer. The nozzles are also different, and they have to be of quite different design. The thread size on their stem varies, so that you can only use them with the appropriate mixer.
If you use propane in an acetylene hose (which you shouldn't), then you _must_ vent the hoses after use. Petroleum gases like propane have a bad effect on the rubber of the hose. Genuine propane hoses (which is orange in the UK, rather than the red of acetylene) has a different inner liner to resist this.
For similar reasons, don't use propane in anything other than a propane regulator. Regulators are expensive to replace if you damage their diaphrams.
Nearly all of my welding is MIG, and I cut with a plasma cutter. Although I've got two oxy-acteylene rigs here, I use oxy-propane for nearly everything (general heating for light forging or bending, heat treatment, oil blued finishes). -- Die Gotterspammerung - Junkmail of the Gods

Sure can.
I got a large tank at the local recycle center (about 18" diameter and about 4 foot tall) that was about half full for $5. They considered it "hazmat" and wanted it outa there- they even thanked me.
I doubt if I can get it refilled, but I'll use the gas anyway.
It does not get quite as hot as acetylene, but propane is cheaper. Don't know the pressure off the top of my head- maybe somebody else can help there. Oh- I was taught to use the "two piece" cutting tip for my Victor torch when using propane.
Hope this helps!

propane MAY work with a MAPP tip, however it won't work with an acetylene tip, buy the correct tip and be done. Also , hoses must be rated for propane, regular acetylene hoses won't do. If you have not run propane on a cutting torch, find one and try it before buying, as propane can be difficult due to it's lower flame temp. If you are using a gas blow pipe for welding, propane will be considerably slower than acetylene. Follow the manufacturer's reccomendation for pressure.