Couple question you got to ask yourself.
1. Will this car be a road car, road/race car, or pure race car?
2. How much can you get out of the car with different suspension?
Can you get more out of the car with a higher spec suspension?
3. Will you have enough knowledge to adjust a highly adjustable coilovers, or have the fund to hire a track side race engineer to adjust the coilovers for you.
If this will be a pure race car, then you don't have to worry about road compliancy and can go nuts on the springs rate. (Granted you got to adjust everything base on the chassis build and the rules that you want to compete in).
Then you need to have the ability to adjust a multi-way (2-way or 3 way) suspension and have the skill to use it if when the adjustments are made.
Another issue I would be slightly worrying would be what aftersales service you need.
Because high end suspension should be rebuild about every season or every 2 years at least, so you got to factor that in also.
If it was me, and at that price range, I will be looking at the Nitron NTR 2way or 3way coilovers assuming I answer yes to most of the questions above.