Transmissions are availible at adsitco.com. But $1500-$1800 sounds about right for a shop to do it. 560's are awsome cars but at 188k it is going to need some work. Think timeing chain, maybe valve job. The suspension could be tight bepending on where it was driven. Mine was driven on the highway a lot so at 235k the front end is still tight. Frankly I'd wait and find a mint 300SD in the $4k-$5k range. Their is one in the local paper for $2950, ad says it is the original owner new trans, radiator, starter, etc. You should look for something like that.

It doesn't sound like you want to put tons of money into it and a 560 like you describe cout eat $3k in short order. Although any old car can do that. If you got it for $700 and put $5k into it you would have an awsome $5700 car, plus you could probably get most of your money back when you sell it.

just my 2 cents.