What's the going rate for a Twitter account name?

http://trumi.net/, a SF area website, just launched and sent me an @ reply saying “I would love to talk about an exchange for your acct name.” I like my twitter account, but it’s not like I have a ton of followers – I could easily switch over, but it’d be annoying… PLUS, if you Google “Trumi,” I’m the #4 link, which is semi-valuable. Here is their account.

I went ahead and emailed back saying “what did you have in mind?” and took the precautionary measure of setting up another Twitter account just in case.

So what is the going rate for a Twitter account name, and/or how much should I ask for?