I'm pretty sure there is a decently wide range of possible costs.. it probably depends on what specific blood test(s) they might run, any possible standard check-up the doc might do, and so on and so forth. It also depends if you have insurance, and whether they take it or not. Chances are you'll have enough money.. and chances also are that if you don't have the money yet, that they'll work out some sort of payment plan for you.
(Hopefully this isn't a rule violation...) Because of my insurance, my doctor appts (normal check ups) are a $25 co-pay.. as far as blood work.. I'm pretty sure it's another $25 co-pay.. possibly a bit more. (my memory isn't the greatest xD)
Good luck, hope all goes well!
-Aven