What's your income worth to you?
brk: If it's a unique opportunity, you should take it.Something else I'll throw in... I've been known to successfully renegotiate my salary several times.  Sometimes as frequently as two weeks after joining a new company.  It can be very difficult for a company to properly value and compensate for technical talent, especially if they have not hired a lot of people "like you" in the past.  It can be easier to come on board and prove your skillset and THEN work out a proper salary.  If you choose to go this route, also keep in mind that you need to make sure your comp is "fair" in regards to other people in the company.  If everyone else is at 60% of market rate, then it's not likely you're going to get 100+% of market rate for yourself.  But if they understand the other jobs and pay scales better and just don't know how to properly comp you, that is a solvable problem...