Since you don't want to spend a lot of money, go with the overhead setup. Otherwise you'll have to buy a Single-DIN radio and lots of other stuff.
Plus, mounting it overhead allows you much more flexibility when it comes to deciding which CB you want to run -- only certain CBs will fit into a DIN slot, and only one or two of those has a front-mounted speaker...
FWIW, I've found the Uniden PRO520XL to be a great little radio. Walmart has the best prices, BTW.
I wanted to run either my Uniden PC68 Elite (w/ Weather and some less-than-legal work done to it) or my Galaxy DX-949 (slightly less legal than the PC68), but didn't have the room.
When it comes to priorities, your antenna and mount should be first. Then make sure you get quality coax cable. Even the cheapest CB will (should...) put out the same power as anything else (aside from 10-meter "export" models, which aren't legal for use on the CB bands anyway...). A good antenna system will make much more difference than a pricy radio will.
2013 Billet Silver JKU Sport S, 6-Speed, TF Leveling Kit, Spidertrax 1.5" Spacers, 285/70R17 Firestone Destination M/Ts on OEM Sport wheels.