How do you judge amp value?

[MatchBookNotes]

hey,
I've got one of the early trayner guitar mate 2's the serial is G-203.
I replaced the caps, speaker (greenback in there) and had a 3 prong put on there. I have all the original parts that were taken out(speaker and chord) the name plate is split and i'm going to fix that, its got a few rough spots but it doesn't look junky. I've put around $480 canadian into including original buying price. I'm thinking of possibly seeing what i can trade it for, is it worth more than what I paid? Its built like a tank and probably won't break down again until the caps need replacing.
thanks dudes!

[Milnoque]

Google your amp and see if you can find similar ones for sale. Gbase.com is another good place to search.