1800 watt amp? rms? max? what era of amps? c'mon dude, when establishing the market value of something you first need to know what it is. what model is the amp.
I'll give you $50 for an amp that you can't even find a model # for or list the specs on. How can you offer a warranty on something if you don't know what it is??
If it's last years model, chances are 1800w is the Max power rating, not RMS (unless it's a higher level RF amp and not the cheesy Best Buy crap).