Purchasing builder home - can you request appraisal?

[Kuba Waszywski]

Last year I purchased a home from a builder which is now almost finished. home prices, even on the same street have gone down, where inventory homes are discounted by 10%. I'm locked into a purchase price from last year. Since builder is providing incentives to use their lender, is there any way to force them to lower the sale price now? for example, going with builder's lender but still request a 3rd party appraisal is done? I could try to go with another lender and they might apprise the home lower, however I automatically loose out on the builder incentives towards closing.