Rated for 6000#? Most trailers are rated by the axle rating. From there, you need to subtract the weight of the trailer frame itself to come up with the payload capacity.
For reference, in SW Michigan, this past summer, I purchased a 9 year old 16' beaver tail flat bed tandem axle trailer with 7000# axles for $1500.
Put new brakes, fenders, wiring, sand blast & paint. Seeking one new tire. Overall, have $2200 invested. Little less than half of a new one.