The rules for lenders are fairly strict, but knowing how to work with the rules can really help. Your credit score is only one issue, your income, assets and job time are others. The only final answer can come from a lender who looks at a complete file, but in the past several years, scores below 580 have very little if any options.
At 580 they exist, but are limited and generally require a higher down payment. Once you are into the 600's your options expand and the higher your credit the greater the options available and the lower the rate will be.
I want to agree with Becky, look into doing some legitimate credit repair. Dispute any inaccuracies on your credit report, pay down high balances to 1/3 or less, use your credit but don't abuse it. Do not close any accounts or pay off any old collections until your lender instructs you to.
Best of luck.