I'm trying to collect one of each of all the 5000 series plugins. Sometimes its just fun to watch what others pay. eBay is the place to sell, but not the place to buy (usually). For me, an AM5030 is a top collectible.
Ebay is not the place for the high value test items. I got a AM503 in a TM501
with the A6302 probe all working perfectly on craigslist for $50. Yes, that's
a single zero.
Anyway, you shouldn't expect this era test equipment to work. If you buy
this stuff, you should expect to fix it. Tek expected you to service it, that's
why they wrote those awesome manuals. That all changed in the 1990's,
try fixing a 11000 series scope; now that's a real boat-anchor.
Once you have a lot of test equipment, it's best to just rack mount it. Tek
and HP rack mount stuff is generally cheaper than the bench units and it's
physically easier to service. The only test equipment on my bench is a
crappy radio shack DMM.
The other solution is to get a model 3 scope cart. That will hold a pair
of TM504 or tm5003 plus a scope. The lower mainframe is a bit too low
to work with though.