For a car in the age range you are proposing you'd be looking at a " classic " Alfa, probably not too many around over there and perhaps not an ideal first Alfa. Why not come into the 90's, gives you a much greater choice and would probably be more reliable.
If you really want to stick to an older car my choice would be the GTV 2.5, a stunning looking coupe with a 2.5 V6 on board, give you about 25 - 30 mpg I would think. They were prone to horrendous rot and at one point had problems with cylinder heads, I think a good one would be hard to find. Of course in the same age range some lovely Spiders, but, again, difficult to find nice ones for reasonable money.
I lived in Seattle a little while ago and seem to remember that insurance costs were pretty much the same as they are here. However as I'm in a slightly older age bracket than yourself wouldn't like to try and estimate costs for you. Perhaps some younger members on here will be able to tell you what they pay here in the UK to perhaps give you an idea.
Get a good Alfa, you'll love it, buy a lemon and you'll be crying in your beer,

once you're old enough to drink !!!
Good luck.