Congratulations! I just got married myself:
As for keeping the costs down, you need to consider what is important. No one, and I mean NO ONE, is going to remember what the dang centerpieces look like. Or the decor. Or what the food tastes like (unless it's horrible).
There is one thing you should not skimp on: photographer. Do NOT hire the cheapest one available. Do make sure they have a second photographer and/or a backup in case of an emergency. Photos are the one thing that you'll have forever.
Next on the list is food. Find something inexpensive. Honestly, I'd go with Chipotle. Seriously. They cater.
As for liquor: don't bother with open bar. That will be ludicrously expensive. Pick 2 or 3 wines, 2 or 3 beers, and both of your favorite mixed drinks. Buy the supplies yourself. Hire a bartender. Return unopened booze products to the store, checking with the store to begin with. (We spent ~$500 on booze for a 75-person wedding, and returned just over half of it afterwards!)
Do you have younger and/or fun people at the wedding who would like to dance? Get a decent DJ who will get people up and dancing. That makes the reception more fun. But if most of your guests aren't into that, just hire someone cheap.
But like I said, a lot of the stuff people fret and stress about at a wedding DON'T MATTER. Centerpieces, decorations, flowers, table linens, plates/silverware. Forget all that. No one will remember them in a month.
Also, someone said printing your own invites. Yes. Do that. That's what I did, and all it cost was about $30 in nice-looking cardstock and paper and another $18 for a toner cartridge on my home laser printer.
And as for using your car in the wedding...