It will definitely depend on the condition and which version of the 5b it is. Is it an original RTR, an SS, or a new 2.0 RTR? If you are unsure post some pics up here, if you can. Is your e-revo new, or driven and "new?" If your e-revo is new, as in not driven fresh out of the box, it might be a fair trade.

Just for a gauge, I've seen original RTRs go for $400 and less. These are ones that are running but more than likely need work, since they have probably been run a while. I've seen SSs go for $600 and less, I saw one with upgrades such as the Turtle Racing clutch setup ($200), go for $600 and it had only been run a couple of tanks. I knew both the seller and the buyer, so I knew the exact condition it was in, and it was in perfect condition other than a few minor scratches that are expected from running it.