Also, most co-op boards look for a maximum housing debt of no more than 28% of your gross monthly income. At $55,000 a year, your gross monthly income is $4,583 - 28% of that would be $1,283. Your monthly payments on a $150K apartment, assuming maintenance of about $600/month would be right around that figure.
If you have any further questions, or would like assistance in your search, I can see what's out there for you. For my contact information, see my website http://www.teammd.net.