I'm no expert in this field either, I have spent the last few months experimenting with different shades of blue and green and lights and lighting positions. All with the same thoughts as you, price is a massive issue.
I started off with a rig made from dowel rod, 8 little 50 watt halogen spot lamps and greese proof paper as a diffuser, the word nightmare summed that up. On a hunch I went and bought a 150 watt security flood light from B&Q for £4.50 yestarday (they sell them at that price without the sensor that gets more cats than burglers). This sits on the floor (The diffused spots are either side and above), it shines up evening out the hot spots that still remained from the spots.
I'm going to dump the spots now and stick one of these floods either side in place of them. The area I am lighting is a sheet of 2.4 meter by 2 meter bed sheet material I got from Remnant Kings for about £6. If you want to light a bigger area B&Q do the same light as 500 watt for 50p more.
I've noticed a differnece between green and blue too, at the moment I have a blue sheet up that is getting changed for a green one. I had a small green sheet I used for experimenting with close up shots before. I got it going good with the diffused spots. With the larger blue sheet I find it picks up on the camera as grey. When I stuck the smaller green sheet in the same shot as this I can clear it out fine without affecting my subject when keying green, when I key blue (wich is picked up as grey) it's close but not good.
So I'm almost there (hopefully as soon as I change back to green from blue) and hope some of what I have found from my experimenting may be of some use.