Motorbike carbs are a cheap (if you can make your own manifold) alternative, and they work really well. I run a set on my race car and my mate has a set on his road car.

They are really responsive and don't choke the engine at high revs. Just have to open the main jets right up and play around with the height of the needles to get them to give a good A/F mix right through the rev range.