What might this be worth?
 

I'm thinking about selling my 240D and getting something newer that doesn't require as much hands-on time. I like my car, and it's a lot of fun, but it requires a level of attention I can't provide when I have other hobbies I like more.

'83 240D, 225K Miles
Florida car its whole life!

Auto Transmission, some flaring 2-3 and 3-4 but has never let me down.
Power sunroof, works.
Manual climate control. Several year old A/C compressor, currently non-functional but due to an electrical issue, according to the A/C shop I took it to -- not the compressor itself.
Good body -- only two tiny tiny spots of rust that I've seen. Freshly repainted a couple years ago.
No rips in the MB tex, seats are springy, dash intact, trim pieces are a little rough (cracking veneer on the wood, door fabric trim loose.)

Has had some significant work done during my ownership, too:

new starter
new glow plugs and glow plug relay
new master vacuum hose
new transmission modulator
adjust vacuum system to correct various problems
valve adjustment, new valve cover gasket
new engine mounts
new transmission mount
new set of 4 tires
new driveshaft flex discs and something w/ the center bearing
new set of 4 speakers
new frontleft tie rod assembly stuff
new thermostat

Doesn't leak fluids, doesn't consume that much oil. (I add a quart or two every couple tanks of fuel.)

The downsides:
Transmission flares a bit 2-3, 3-4
Kickdown could be adjusted better.
Some blow-by (to be expected, its an old engine)
cruise control doesn't work, actuator is not currently even installed in car. have spares of unknown condition of actuator and amplifier, though.
A/C doesn't work due to an electrical gremlin of some sort.
Gets very high temp at highway speeds (115C), but is okay at city (90C)
thermostat housing has a bolt sheared off in it, currently held together by 2 of 3 bolts for about a thousand miles, doesn't leak at all.

Gets 24 MPG, last 3 tanks.

I bought it for $5k and have put $2500 of work into it...hopefully its worth at least what I paid for it.

where are you located. Location can make a differance.

Orlando, FL. Car is a Florida car its whole life, Gainesville and then Orlando.

I don't want to rain on a forum buddy, but I doubt seriously that you will get much more than half, if that in the condition described and being an automatic.
If time is no concern, you may get more than 2 or 3 large, but to motivate somebody to buy it will require a deal.
Just ebay it with a reserve you are comfortable with and see what happens I guess.
I'm just basing that on what I pay, have paid or would pay, and was meant with total courtesy....:)

rust is bad, a bad respray does more harm than good in some cases. Tranny flaring and no AC on top of that makes it a 2k car, topps. I doubt 5k is realistic, but this summer you may get top dollar for it on ebay. Especially if biodiesel is cheaper than Dinodiesel.