When I have to rebuild the engine...
 

...because my crankshaft has play, what are my options, costs included please, for a '91 944 S2 Cabriolet? Thanks much!

What do you know or what have you measured to know why the crankshaft has play? Have you miked out the block and crank and inspected the bearings? It could be you may need a complete motor or as simple as new bearings and a rebuild - hard to tell with the skimpy info here.

I just spent the winter resolving the same issue on the engine of my 1989 S2, thrust bearing was worn on the front side. I found out I had an issue because under heavy braking the clutch pedal would get soft.
http://i115.photobucket.com/albums/n...d/IMG_2021.jpg

Quickest option would be to buy a used engine, I've seen prices all over the place lately from $2000-$4000 depending on mileage. If you have a shop pull and rebuild the engine I'd think it would cost a minimum of $5000 for a full rebuild, probably more like $7000-$8500 at a reputable Porsche shop. I pulled my engine last November and spent this spring rebuilding in in my garage with some work being done by machine shops. I haven't totaled all my invoices up but I figure I spend somewhere around $2500

That sounds about right. Thats about what I plan I spending on my rebuild.

You know, it's too bad we can't spin in new thrust bearings with the engine in the car...

This is what you need for sale on RL asking $4,ooo.oo.Been done with sucess a number of time.:Dhttp://forums.pelicanparts.com/uploa...1278102070.jpg
http://forums.pelicanparts.com/uploa...1278102093.jpg

Top marks Krazykarl on the DIY comment,if you have the knowledge to do it yourself you can save alot of money,best to take your time check and double check along the way,label and bag clean parts and use the resources on this site.
You will need to check the thrust faces on the crank for wear ,once the white metal has gone its a hard face wearing on a hard face.
IMO the Porsche dealer overhaul is a money pit (you pay) as many parts are changed because the "book says" and not based on the real condition of the motor,you pay to cover them!!.