Your loan amount isn't dependent on your credit score. In other words, if you are borrowing $75k or $375k, your score, income and assets will all need to qualify. Larger loan amounts require more income and possibly more assets to get approved, but the scores to qualify will be the same.
Generally depending on your down payment and other criteria some lenders may consider you as low as 580. Most will want 620 or better. As your score goes up the rate you are offered will improve as well.
I suggest you sit down with a good local mortgage lender and discuss your situation. As a lender I often assisted buyers work through their credit issues to get them qualified or improved for better rates & programs.