If you really have a limited budget, buy a used bike. 2 or 3 years ago, I got an old Specialized Rockhopper with rigid forks that works great for touring. It had hardly been ridden. I put on "city" tires, a new saddle, bar ends and a rack. Total cost: $60 for the bike, about $100 for everything else. There are many brands of mt. bikes that would have worked as well as the Rockhopper, just get one before they put on suspension forks.

Last week I got a Trek 790, also very lightly used, for $200. It needed fatter tires and a wider more comfortable saddle - that's all. It is already geared for touring and had a rear rack. I replaced the cables and handlebars, but it didn't really need it. I'll have about another $100 into it when I'm all done.