Where to start here?
First off if you are contemplating buying an early Porsche then get it inspected by a marque specialist who knows these cars.
As for rust : outer sills, intermediate sills, jacking points, front suspension/ fuel tank support, lower part of inner wing adjacent to the A post, lower part of B post, kidney bowls, area around torsion tube at rear, floorpan especially the edges and around the pedal box, lower corners of front and rear screens, rear parcel shelf and rear seat pans, around the headlights, lower corner of front wings adjacent to the A post, door bottoms, plus other 'surprise' areas. In short lots of places. I have only detailed the typical ones.
Part restored could actually mean part bodged unless someone familiar with the cars has done the work.
A T will cost as much to restore as an S and is of lesser value.
Most replacement metalwork is available but beware like all Porsche parts is ridiculously expensive. Most suspension parts are available as are body seals and rubbers. Engine cylinder, pistons, con rods, valves, tappets, crank bearings, oil seals, gaskets,
etc are readily available as are exhaust systems. Interior trim, and carpets is readily available. LHD dashboards are available but cost around £900 and are of variable quality. Some parts are only available second hand so suggest you join DDK-online and early911sregistry.org which are the early Porsche communities in the UK and USA respectively. On DDK you will find build threads and can see what other owners have had to do to restore their cars.
There are well known specialist who work on early cars: Autofarm and Tuthill being just two. There are others of course.
Early cars once sorted are extremely reliable, relatively inexpensive to maintain and wonderful to drive.
I will not comment on prices as it is "how long is a piece of string" situation. Depends on the condition and completeness of the car, how much history it has etc.
Good luck.