First, I wouldn't get too excited yet that you would even qualify for a mortgage with that low of a score. Yes, some lenders will do an FHA loan with a score of 620, but, most now want the score to be more in the 650 - 670 range.
Also, what is holding your score down? If it is unpaid collections etc, you are going to be required by any lender you go to to clean those up and pay them off before they would promise you a mortgage.
Your interest rate is not based on your income, it is based on your credit score and report.
640 is the minimum cut off for home loans. 640-680 is the extent of subprime lending. Below that isnt worth discussing.
Mortgage rates for well qualified applicants is about 4%. In your range you can expect to pay around 5-6%. This may not seem like a lot but over 30 years it's a lot of money.
If you can raise your score, your income would allow for about a $150,000 home if you do not have other debts. This also depends on taxes and what insurance is required as well as monthly fees if applicable.
Typically 3x your salary is about what lenders will afford you but this doesn't mean you'll be able to afford it.
A home is a huge decision. Aside from getting approved for the mortgage remember other costs involved. The typical home requires $3-6,000 in repairs each year and the cost of utilities is greatly increased from that of a condo or apartment. If you know someone who has owned their own home or afforded multiple homes, I strongly advise you to speak with them.
Another thing to remember is a realtor is not your friend. They will sell you a house 10 feet under water if they can get away with it.
Good luck, check out the below sites for more credit help.