Dude - get otta South Arlington & hit the HPs in Dallas (but not Mesquite). I usually score something good, and since you don't have that much vinyl right now, your odds go up considerably. Hit the main store on NW Highway first, and look in all the categories.
Of course, there's plenty of Goodwill stores (including a bigass one is S. Arlington, iirc), and if you're looking for Brother Dave Gardner LPs, hey, that's the ticket. But sometimes....
And yeah, Dusty Groove carries vinyl, new and used. Just be careful of anything used that's rated lower than VG+ (and even then if it's a "hot ticket" item that seems reasonably priced). If the rating is lower than VG+, and the prices is less than the cost of a full-sized fast food meal, then it's probably worht a shot just to get a play copy. Otherwise...
Of course, now that you're consciously looking for vinyl, anytime you travel, plan your meal breaks (times & locations) around used record stores. It's a good way to "walk off" the meal.