[sc_rufctr]

With 190,000 miles you'll need the list bellow for sure and maybe some machining work to fix the PS Bearing support area in the case.

x5 Synchro rings
1st and 2nd gear dog teeth.
1st/2nd gear slider
3rd/4th gear slider
2x Differential support bearings.

Note: This list does not include brake bands and blocks for each of the gears.

When you have your gearbox. Start a thread and post some pics.
There are some very talented and experienced people here who will chime in and provide advice.

Porsche Trans Tools... You can make most of these. Lots of info and photos in various threads here.
You'll need a good torque wrench and a normal set of tools.
Lastly... A clean work area.

So looking at the list you could do it for about $2,000 US. Maybe a little less if your gearbox is in good shape and doesn't need any machining.
You'd call this a refresh not rebuild.

But this could soon blow out to over $3,000 if it does need machining and more parts like dog teeth for 3rd or 4th.

If there are any issue with the final drive and differential then it can soon go over $4,000 because this would best be left to the experts to resolve.
You could re fresh the rest of the gearbox but to set-up the final drive you need some very special tools.