Others have given you advice regarding bike fit. I'll address affordability.
At least in my neck of the woods (Northern California) ten-year-old Cannondale mountain tandems show up pretty regularly on Craigslist for prices around $500. With some slick or semi-slick tires these bikes make great budget touring bikes; very durable and comfortable on a wide variety of terrain. One of these in a medium size might work out well for you.
Brent