On one single kit, I bought a sealed inside MPC 1968 Color Me Gone funny car, I paid $500, sold it a few years later for $500
I have a limelight 1970 Cuda promo I paid $600 for it. both were probably close to 10 years ago
I just bought a nice built Charlie Allen Dart AA/FC maybe 3 months back and I think it was about $150
As a general rule, if it's something I really want and I can afford it at the time,,,,,the sky is the limit.
But generally I keep it in the under $30 range for readily avail kits and/or builders/builtups. I usually look for older annuals than I so for more recent re-leases