You can go after a 4*, but once anybody sees a C prestige is on him, he'll be gone in a heartbeat.
I've gotten recruits as high as 19th for their position, usually around 100 or so overall. You can get in the double digits for overall rankings (think I've landed someone in the 80's a season or two ago, may have been C+ then), but you run the risk of a BCS school coming in and taking him away usually.