Are your cost estimates for repair of an SL in the US?
1) $400.00 to repair a Top that doesn't work! In my neck of the woods it would take that much to diagnose why the top doesn't worK. Also, it would cost around $30 to refurbish one top hydraulic cylinder x 12=$350 plus $50 shipping is already $400. How about the cost of labor to R&R?
3) Redo the seat for $225.- MB-tex front seat cover cost around $350.00 plus labor.
I have no doubt you can do it at that cost, I'm just wondering how.
I also am questioning those price figures.
If you don't DIY, then a fair price for the convertible top cylinders including labor and a full set of Dennis rebuilds is around $1100. Dennis charges $35 per cylinder, and figure $50 in shipping charges because they're real heavy, so you're at $500 or so just in parts, even if you DIY. And $ you $ can $ forget $ buying $ new $ ones $$$$$$$$$ ($3k).
A new convertible top is $400-$600 online, and labor is another $800 or so. It's a massive task, if you did a DIY it will take you at least one full weekend, maybe two.
Timing chain guides, are another $400 proposition if you don't DIY.
A suspension rebuild, using Lemfoerder or OEM MB parts (which trust me, is the ONLY way to go on anything with rubber in it, like ball joints, control arms, etc.), together with new shocks and strut mounts, is another $3-$4k proposition, with most of the cost being the parts. And unless you're really well equipped at home, then most of this isn't going to be a DIY-able task, since you need a lift, a spring compressor, etc.
I mean, don't get me wrong, I would still buy the car. The R129 is great, and you'll enjoy it. But still, keep your eyes open about what you're getting into. There are the few guys around the forum who will swear they've only spent $11.93 over the last 10 years on maintenance, but I don't really believe them and you probably shouldn't either. Cars like that either have not been driven much, or are the ones that I could spot probably $6k worth of needed work within 2 minutes of looking at it.
In the grand scheme of things, it's not that expensive to maintain an R129, if you have decided you want to own a Mercedes. Compared to other Mercedes models like the W140, the W220, or the early W211's, the 129 is actually a very economical choice. But even so, $9 to fix timing chain guides, redoing a leather interior for $200, etc., are really not realistic expectations.