I read this thread yesterday, but debated whether to reply with my ha' penny worth. After casually mulling it over for a day I decided to reply.
Let me be frank... despite what it may sound like to some.
The car's a rust bucket worth maybe $3k - $6k max as is, and I'm being generous I think. It will probably be of greater value by at least another $3k as a parts car.... if parts are dismantled and sold to the right market (e-bay, or W113 websites) where buyer's know the value of the parts and their condition.
One reason for the price being low as is, besides it being a rust bucket, is that it's a 250SL, not a 280SL, and I say this even though I own a 250SL and believe they should have higher value than the market actually gives them. If it were a 280SL it would be worth perhaps as much as $8k or $10k... as is.
One can argue with my estimates of value as is but it will be to no avail until the owner tries to sell it anyway.... then if I'm wrong, I'll love it.
Next... the value beyond the market price is soley sentimental, therefore whatever value sentiment has... which can be enormous, but don't confuse that with market value.
Let's say for example the sentimental value is sufficient to keep the car... then the question is how much one is willing to invest to take it from it's current level to some drivable level and eventually perhaps to a cosmetic level. It won't cost a lot to get it to a drivable level... the greatest expense for that probably being in the work to take care of the rusted portions, with maybe another $1500 to $2k or so in engine and drive train, fuel system, brakes, tires perhaps... assuming rats haven't been at the harness. I may be underestimating here in fact, depending on who does the work and whether MB OEM parts are used or whether some others.
Finally to get it to a reasonbly comfortable level of cosmetic appeal, it needs a paint job and new interior ... you may be able sparkle up the MB Tex seats as is with no serious detriment to cosmetics. I'm guessing the softtop will need to be replaced and someone should look into the storage compartment for the soft-top to see whether that's also rusted out.
So, the work is either time spent + parts, or labor costs + parts. In other words, to get it to some comfortable, cosmetically decent level with reliability will cost a pretty penny... say up to $10k minimum. In that situation you have a $4k - $5k current value plus $10k to bring it back a bit or say $15k worth into it (I can't discount the current value since that's money you or your father would otherwise have for something else).
Now, my opinion beyond that is that to make it worthwhile to spend anything on the car at this point is to take it all the way... and you're talking $30k - $35k in expense, including long block engine rebuild by Metric Motors in LA ..... not a premier show car, but a true beauty and reliable transportation. Add this to the current value of say $5k and you're talking a total invested cost of $35k - $40k or there abouts.
If you've got the money to spend to bring it back to this level, then by all means do it. If not sell it for parts or to someone that can and is willing to spend the $30k - $35k it will require to do so.
Oh, and it's market value may be worth that when it's done, given enough time goes by, otherwise you'll have approx. $5k - $10k more into it than you can get at market value, best case.
What I would be sorry to see though is an original 250SL 4 spd get botched up by a hack job. There are few enough of the 250SL's around anymore as it is, and only a little over 5k were manufactured at all. What I'm not at all sure of is whether there's anybody that want's to invest in restoration of a 250SL in the 1st place though. Most of the market's interested in the 280SL's and to a lesser extent in the 230SL's. Whether the 250SL's will ever garner the market I believe they actually deserve is another question.... my opinion on this is due to it's classic style with all the prior accouterments of the 230SL, but with the engine performance (not displacement, but net road performance in practise) and suspension (and modernizations) of the later 280SL. In my opinion the best of both worlds --- since I don't prefer many of the changes and cost reduction items the 280SL's introduced. ... just my tastes, not to offend.
Like I said, just my ha'penny's worth.
Longtooth
67 250SL US #113-043-10-002163
'02 SL500 Sport