I agree with pnj... There is nothing on your bike (except perhaps weld it) that you can't do yourself.
A bike is nuts, bolts, and bearings. Bearings need grease, everything else basically needs the right kind of wrench. For that 45 bucks you could buy half the tools you need and get some good grease and a few rolls of paper towels... and some Simple Green.
Look at www.bmxtrix.com
-> how-to -> fix your bike -> tools needed (sorry, none of the rest of that section is really done, except axle replacement & wheel building)
There are a few tools, most of which you likely already have in your home, that will really let you work your bike over nicely.
Then feel free to Google your question (first) then ask here if you still have questions (second). Take some digital photos and post them if you have something specific that confuses you.
But, for $45.00 a mechanic will spend about 30-40 minutes going over your bike. That's ALL! No extra work is done, no parts are replaced, it is just a once over to make sure things are smooth. He will spray some lube into cables, and may tighten bolt or two. But, he won't replace anything and will look for stuff that needs to be replaced. Your bike will come back to you a little more smooth than it was, but in a month it will be loose again. YOU on the other hand can sit in the garage/basement for two hours and really do some serious work to your ride. Including everything the bike shop did, but also regrease bearings if you need to, or replace your tires if they are bald.
Online shops, like Dans Comp, will sell you new parts for about 33% less than the store will, and you can use the extra cash for a good set of steel tire irons, or for some Taco Bell.
You CAN do it yourself if you want and you should ask questions before you begin a project so you will have all the parts you need ahead of time.