So while backing into my usual parking spot this afternoon, I bumped a large metal beam that supports the parking structure.

I checked the rear end of the car and found a horizontal dent on my trunk lid. I tried opening the lid to make sure there wasn't any further damage besides the dent (no paint scratches!). It is a bit more difficult to use the "button" on the trunk now...

This is going to bother me and I was wondering if anybody had suggestions on fixes or if its worth it to get a quote from a collision place (never been to one before).

You might try a 2x4 or other suitably shaped lever from the inside after you remove the access panel. Other than that, I'd leave it to the pro's.

Hard to say without seeing pics of the damage. Odds are the collision place is going to give you a pretty high estimate unless you know of one that will do good work (ask around). I'd say keep an eye out for a deck lid that's in good shape at your local junkyard, then have it painted. (This presents some challenges as far as color matching if your paint isn't in good shape.)
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Robb R, 1989 740 Turbo 200xxx

I'll get a picture of the damage tomorrow evening. Visually, it's not much at all and no paint damage *(the overall paint on this car is in good shape). I'd just want something to free up the lock mechanism.

I may call up some places to get estimates over the phone.

In that case I'd say body shop. My only concern would be if they pull/hammer the dent too fast, they'll crack your paint. And if you're not concerned about the actual dent, you may be able to remove your locking mechanism, make sure everything is straight and unbent, reseat it and that might take care of it.
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Robb R, 1989 740 Turbo 200xxx

I'll start researching body shops in my area (Houston). I don't think it should be too expensive considering I don't need paint work, but maybe not. I may have them remove some minor dents located above the center of the trunk lid as well.