Best bet would be to check the local Craigslist for pricing. A running 20 year old rider in good shape by me would be upwards to $500-or so in season. I had a service customer pay $700 for a rider much like what you have, except the less than scrupulous seller on CL they bought it from just cobbled the heck out of it and then she paid me 300$ to bring it up to snuff. They SHOULD probably sell for closer to $350 though.

That era mower with no attachments , I believe Tom is spot on in my opinion ! :) .

You might make more by selling the parts online. There are not many people going after antique riders......

I certainly wouldn't consider a 1998 Craftsman an antique.

If I wanted to buy one to use myself I would maybe pay $300 for a used 22 year old Craftsman in good condition. A brand new similar rider can be bought in season for around $1000.