By far the biggest issue on an 1800 is rust. They rust severely given a moist climate and especially salted winter roads. Bad rust is not economically repairable - good 1800's (they can be found still) are much cheaper than the expense of replacing body panels and repairing frame sections.

Check for rust (and bondoed over rust) here:
1) Sills
2) Front fenders - over headlights, back lower edge
3) Floord bards - pull the carpet to the side
4) Front edge of the frame where the front bumper mounts
5) Front jack points - under your feet when sitting, behind the front wheels

The AC system is a money pit unless it has been converted to R134a (modern stuff) otherwise figure on a conversion job once it needs a recharge - I think the cost of a R12 refill is more than the conversion now anyway.

If it has an auto tranny it is a lot less desirable for most people - if it has an OD make sure it shifts in and out (and back in) properly. The drivetrain and mechanical parts on an 1800 are pretty much bulletproof - especially with 93K miles. Unless its been abused and not maintained at all it should be in fine shape. Compared to a modern car this probably won't feel very quick - a '73 with the somewhat hobbled 'F' engine isn't light on its feet, especially with the dreaded auto tranny.