You really don't want this car for the money. It's a nice car the 78 300, however, there's no turbo, nor (more) modern climate control. The power with an automatic is not for the modern driver (or first time Mercedes buyer) I feel you would have a better time with a turbocharged car.... Better flexibility.

Look into later W123s, 116s (if you can find them in good shape) or possibly a 126. Any of these cars can be had for the Sub $5k in really nice working order.

Remember, there are no cheap cars. It's hard to get away with anything with these cars, the more you put into them, the better they are.

And please, have a mechanic look at the car before you buy. If you don't know what to look for besides the obvious (leaks, rust and wear) you're in for a money pit. Good luck.