I actually picked that exact same trailer up 2 weeks ago for free. Mine has a "Leaf Vac" mesh enclosure with the in-tube hole at the top that mounted right onto the top of this trailer. It came with the older 81 IH Cub that I also suprisingly got for free. The mower had a leaf vac shoot attachment, then to a tube that went to a small HP Briggs motor that was mounted with a plate on the back that then went into the trailer.
Based off of what trailers go for these days and if it's in good shape, I'd pick it up. That is, depending on what they're asking for it.
Realistically, I'd offer $30 for it. If you had to put new tires on it, it might run you 50 bucks. If you bought it and had to do this, you'd already be more then halfway there to buying a trailer that's in better condition on craigslist or fleabay for $100.