I'm reading this board as I'm hoping to be able to afford a low
mileage recent Miata....but until then, I have my 14 year old Honda
with a lot of miles on it!

Meanwhile, to your question...7 years ago I bought a 4wd pickup (a
Toyota) which did not have A/C. I had aftermarket R-134 done to it and
it's been perfect, very cold, works fine. Can't see why it wouldn't
work out well in a Miata, too...

A Dealer can install a/c for you. Or if you are mechanically inclined you
can get a system from a wrecking yard, install it, and take it to an a/c
service place to get it charged.  1994 and newer systems are R-134
refrigerant.

1994 is the first year of the 1.8 motor and the last year of a working
factory oil pressure gauge. If you really like your car, at least you know
it's history. If you get another you may find unexpected problems.

On the other hand, if you have deferred replacement of the cam belt and
service, and your car need tires, brakes, clutch, top, etc, it might be more
practical to sell your car and get a car you like with low mileage and less
in the way of pending service.