I just picked up a superb Top Tip off "teh intarwebs" on how to make DIY "ink" wash for weathering etc. The kids buy Games Workshop washes at £3.50 per pot, I reckon a lifetime's supply of the DIY brew would work out at less than one pot!
I tried it, it really does work. Amazingly simple. One part Johnson Klear floor sealer, four parts water, shake, let it stand for a while and then you're ready to use the clear base to make any colour wash.