[geshaghi]

Take a look at the for sale section. While I think $400 is on the low side, it isn't unheard of. The trombone cooler that you have isn't particularly desirable. I usually see these setups (with a trombone or radiator) sell in a range between $500 - $750. Issue tends to be condition and location, as shipping can be expensive and a real PITA. A local buyer will likely be willing to pay more than someone who needs to have them shipped.