A couple of thoughts here.
Photographing your artwork is one way to go. There are large flatbed scanners that can digitally reproduce your work better than any photo for good reproductions. The initial work is a bit pricey depending on the size of the work but you can't match the quality.
As far as trying to start a business that way, may I make another recommendation. Get quality paper for your printer and make postcard or greeting card sets and try to sell them in stores or online. Let the public get to see more of your work at a more affordable price before you go for posters, canvas reproductions or any other expensive method.
As far as printing goes, Lithography is a form of printing/reproduction that you can consider where your poster sized copies on decent paper can cost under $2.00 a copy and if you have to buy 200 to get that price because they only litho in quantity then heck consider how many copies you get for that money than with a canvas copies. The cheaper your cost the cheaper you can sell the piece and make more money in the long run and get more copies of your work out there.
Good luck. Post samples of your work.