Tough question.....Not running absolutely KILLS the value. A RUNNING 230 in average condition w/o implements sells in the general neighborhood of $4000 to $4500 here. Add/subtract for good/bad rubber. "Needs injector work" is a broad statement. Is that injector cleaning or a new injector pump....? Can be anywhere from a simple DIY fix-it to a very expensive shop visit. ($100 to $1500 fix????) That sort of problem scares the bejesus out of most folks and simply turns away those who know what the problem CAN involve. I'd say it'll knock the value down to less than $2500. Loader adds $1000+ to a tractor of that nature. Maybe more on a GOOD tractor. Box blade adds MAYBE $250/$300.
Knowing MF230's and how they sell here, along with what info you've provided, I'd walk away from anything over $3000.