First of all, there are many different types of annuities. Some are okay for the right person in the right situation; others are pretty much terrible for everyone regardless of circumstance.
So first of all: What kind of annuity is this? I'm guessing it would be an "immediate annuity" or an SPIA that will provide monthly income upon retirement. (This, IMO, is a type of annuity that can make sense as a partial retirement income solution for some folks in the right situations.) If so, there are several places on the Web to "price" these -- usually you enter your age and gender along with an amount to buy, and they spit out the monthly payments you'd get for life.
You need to consider your needs and make sure you're comparing apples to apples when it comes to things like income for surviving spouses and inflation adjustments (if any). Generally this is a pretty bad time to buy one because the monthly payout is largely tied to long-term, high-quality bonds. The lower their current market yield, the lower your payout.
"Hey, for every ten dollars, that's another hour that I have to be in the work place. That's an hour of my life. And my life is a very finite thing. I have only 'x' number of hours left before I'm dead. So how do I want to use these hours of my life? Do I want to use them just spending it on more crap and more stuff, or do I want to start getting a handle on it and using my life more intelligently?" -- Joe Dominguez (1938 - 1997)