Hey Mitchell, good for you that you're thinking of doing something like this to further your career.
I'd say you need to first start shopping around to see where you might be able to get these posters printed at a cost that would allow you to turn a profit. Second, are your images worthy of people buying them? You need to look at what everyone else is doing and either make your images stand out, or find a different angle so your images make people stop and notice.
Put together a portfolio of only your best images and go around to a few of the local gas stations, galleries and gift shops to see if they'd be interested in carrying some of your stuff for you. Remember, that many of these places are either going to charge a commission or are going to want a cut of the profits, so make sure you have this worked out and have it in writing before you start hanging your work up anywhere.
I'd also look at Post Cards and simple things that people are more apt to buy than a big, poster type print. The book store we work in sells a few hundred post cards every day. I cringe because many of them arent even that good of images and I think "If only I could slip a few of my own images into the display racks!"
When you start ordering post cards in bulk, the prices drop considerable. Talk with Luca or Jana as both of them have some great post cards that they sell in their hometown areas. They can probably point you in the direction of a printer that might be able to help you get started.
Good luck, and hope you start earning some money off your work