Motor: If you are doing the recommended 3-year maintenance, or worse yet, the accumulated maintenance over a 3 year period, and having it done at a typical shop, get ready for a shock.
My Yam F115's 1 year service was something like $400 US. In looking at what was done, the only thing that gave me any pause was the impeller change, which turned out to be somewhat involved, but easy enough to do on my own.
As to the trailer, I'm not really sure what would be done to service it. Could be anything from "check for loose bolts and check tire pressure" to "replace and repack bearings, change brake shoes, grease everything else, retorque fasteners". Dunno.