This is indeed a really complicated question. Affordable is as affordable does. I'd spec
Selecon Pacifics as my favorite
conventional instrument, they run about $300 each, and of course have about 12 options for lensing not counting zooms. So a lot depends on where you're putting them and what you're lighting. As for
LED units, you can get cheapo slimpars in the range of $25 each if you don't need the light to look too good - if you just want to turn a wall red or green, and don't need to have even fades and colors or so on, you can get tons of
LED units from china for practically nothing. On the other end, I'd spec the
Selador units for color washes where you want a beautiful mix of colors, but those are $1500 a piece or more...
Maybe give a little more detail as others have suggested - dimming already installed makes a big difference in cost/value of incandescents vs.
LED units.
Power supply is a big aspect as well. You might find a local designer or
venue to check in with a professional on what your needs are. A lot of sales houses will come out and look at your space and discuss options with you - it's not a bad idea to get two sales orgs to offer competing bids for what they think you need - but you'll want to really decide what your needs are.