Where else would you buy a new trailer? Expect to be able to negotiate a significant discount from MSRP. I'm out of touch with trailers, but on motorhomes the range is 20-30%, depending on how eager the dealer is to sell, and other factors.
Edit: The OP edited his original message from a new trailer to a used one.
You may try looking at Craigslist, RVtrader, etc.
Many of the ones you find will be listed by a dealer. Best advice is decide what weight trailer you can tow. What floor plan and amenities you want. Then, just shop from there for the best deal you can find. You can use the NADA guides online as a reference of values on the used trailers you find that fit your needs.