Lots of suggestions here thanks everyone! A couple general things I want to comment on.
I didn't mention it, but I do have a truck and trailer to make outings easier, but I would prefer not to have a car I can't take for a test drive on local streets. I'd hate to book a track day and find a small problem I could have already fixed with a trip around the block at home. The lighter the car the better, since I'm only using a midsize truck but generally the suggestions here all fall into that under 3500lb category anyway.
Convertibles and safety legality in general - Once a proper roll bar has been added, is a hard top also required? I'm looking at HPDE type events, lower level track days and weekends. A hardtop for an NA/NB Miata is fetching double what it once did, NCs are hard to find, and I've never looked for one on a Boxster but I know they exist. Almost makes me want to go for a hardtop platform to start with, but some of the options here are hard to overlook.
NA Miata - Using the car I currently have would have me spending roughly $5+k to bring it up to snuff for track use. Part of the idea here was to see what other options I have for similar money assuming I sell the car and bring some cash to the table. That doesn't rule out selling my 1.6 and moving on to a 1.8, short of having an automatic car I have the worst starting point open diff, small brakes, 1.6, no roll bar, no hard top, tired brakes, old tires, etc.
NB Miata - I did find and contact the owner of the orange and grey car posted here! It felt like a good option to fill the role I am looking for. Shortly after my excitement faded away when I learned that NB cars suffer from some major rust problems in the front chassis legs. They rot from the inside out with only minimal rust showing from the exterior. I didn't realize this change in design from the NA and being in an area that uses tons of salt I'm a bit weary of the NB now. I've seen many with rust issues in the rockers, and I bet the front ends aren't much better.
NC Miata - I see the occasional NC1 in the $8-9k range, but almost always 5-speed cars. Do they have more issues than the 6-speed when used on track? I know the early 6-speed isn't the most robust and the 5-speed is a carry over from the earlier cars. I like these as a starting point. I have owned one before, and I think it might be a good fit, but cheap NCs aren't very cheap anymore.
986 Boxster - I haven't looked into these much, all I recall is the IMS issues that plagued some. How do I find a good one?
86/BRZ/FRS - Not finding any under 13k in my extended area, 250mi plus. Most of these are rough. I like the platform, but they might need to age a little more to get some breathing room under $10k.
E36 - Another one I like, but availability is slim. These appear to be the new S13 of the drift world and I'm not seeing much worth buying.
E46 - I do see some nice rwd, manual cars, but rarely the nicer upper trims, ZHP, etc. I've also been warned a diff is a major expense for one of these cars, like $4k. I'd like to have an LSD for this purpose, but what do the owners say? I would enjoy a straight six singing along on track.
E9X - A few of these are getting into my price range, but BMW really ratcheted up the sales of xDrive models by the time the generation came out. Is it worth messing with an AWD car? Not finding the rwd, manual models to be available. I think I also read of a spec series on these starting up?
8th Gen Civic Si - One of my personal curiosities, a potential spiritual successor to my GS-R. I see some in the 6-9k range. I don't know much about how they handle track use, but I would assume quite well.
Fit/SundaeCup - Of those that run in this class, I like the ethos of what is going on. Can you tell me, would the 1.6L miata I have now be faster or slower given the same driver?
ExRacecars - I've seen some interesting things here, a $5k late 90s accord, a $3K Mazda MX-6 usually with spares too. I like the idea of having a real cage, but these are odd ball lemons and champ cars. Getting one to pass as street legal in PA would be a chore unless you guys know something I don't.