For $200 I'd say anything made by pioneer. Make a list of the features you want, like aux inputs, usb ports etc. then do a bit of research. I found my pioneer off ebay for like $45 bux, so you can def. manage something decent with your budget. As far as putting a single din in the oem spot, its easy as pie. This is what i did.
My pioneer stereo was a press fit into the oem spot widthwise. Mine had metal tabs you can bend out to stop forward movement. That, and two pieces of electrical tape used as shims, makes it a perfect fit. To cover up the hole made by difference in height, I cut a piece of plastic off a broken old printer, then used a dremel to trim it to a snug fit. Jb welded a metal clip to the back of this piece. Painted the bezel and plastic piece with some silver rustoleum I had lying around. Then the whole thing "snaps" into place. The stereo faceplate covers up the seams and the end result looks like it came stock, or so my friends say. The good thing is, I can pry this whole thing out with my buck knife when ever I need to access to the back of it.
Of course you can go to walmart and buy the plastic fantastic scosche trim set. But I like to do projects, and this way I also saved $20 bucks, which I then used towards speakers. If you are going to attempt the wiring yourself, I highly suggest buying the wiring harness adapters for Rangers so you don't have to chop up your truck. Its like $8 bucks online or at wallyworld.
Sorry for the long post, but I hoped this helped.
2004 4x4, ex-fleet vehicle. 4.0 v6 with 110 k, 4.10 gears.
Modifications: Whelan hidden strobes, Ion 174 alloys, yokohama geolander at 235s, billet grille, airbox mod, Dynomax exhaust. slight torsion crank. More to come!!