I understand when you say "middle model" I am taking it that you are talking about a model that might not have all the options that came from the factory? Since you want to scrape I'm thinking you also want to lower which means coilovers?
The first gen (NA, with pop-up headlights) is going to be the least expensive, based on condition & miles. 1990 - 1993 was a 1.6l motor and 1994 and above went to 1.8l. If you start looking around on Craigslist and eBay, you'll see examples from $1000 (rough) to $6000 (nearly mint) with varying mileage. If you are willing to pay a bit more - $7000 - $9000, you can have an already modified turbo/supercharged Miata. If you are patient, picking up one of these is the way to go because you can quickly tell if the owner took care of the car.
I picked up my 1995 for $1700, but it needed a new clutch and I did a timing belt kit along with all the fluids. All of that ran me another $1000 or so. The car was well sorted after that work - been solid for the last two years.
The second gen (NB - with fixed headlights) can be had for a little more as compared to the NA, again depending on miles. Prices can overlap with the NA especially if you are buying an already modified car.
The MazdaSpeed is a factory turbo model and is available on the NB.
Third gen is NC and those body styles are quite different than the NA & NB - they look sort of like the new RX-8 to me. These are still pretty high in price because they are still so new but there are always deals if you shop around...
All three have many many options for coilovers. The NA and NBs have been around long enough that there's a huge aftermarket product base. You can go as low as you want - but you might want to also invest in a skidplate!
Welcome to the site and good luck with your search for your Miata.
If you want a Miata that scrapes, just put something on the bottom of your car, so itll scrape everywhere. Duh. That's what I do. I've got a huge metal plate welded under my car, so, even though I'm at stock height, I can scrape everywhere.