Could anyone tell me where I can find prices on a 4gang meter cabinet and an 8gang meter cabinet? And also 400 amp main breaker and an 800 amp main breaker?

This is the best you will find on the web:

SearchResults

And these prices are a bit bogus.

Electrical equipment such as this is usually on available from electrical distributors, and pricing is mystical.

To get the best real pricing, go to a local electrical distributor, that will give you a real price for exactly what your looking for. Try to find an independent firm, as most of the large chains, such as Graybar, Wesco, CED, GESCO, etc. will only sell to contractors with established 30 day accounts.