Check out craigslist.com for used bikes. Knowing your size will eliminate alot of the listings that will not suit your needs.
As far as sturdiness, just pick up a bike that is not rusty. Most wheels haave spoke counts of > 24 (front) and 32 (rear) which will hold your body easily. You can also check out the Clydesdale section of the forum for additional ideas and suggestions.
Otherwise, welcome to BF! now get out there and find a bike so that you can go riding!
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Women think they're so clever because they can fake an orgasm for the sake of a relationship, but men can fake a whole relationship for the sake of an orgasm.