You can probably only afford a co-op that costs about $150K or so. As an agent in Forest Hills, I know that the majority of the co-ops here require a 20% down payment (which pretty much caps you at $150K if you only have $30K in the bank). Also, once you close, most buildings require that you have at least 6 months of mortgage plus maintenance left in the bank as reserve funds (they do consider $401K and retirement funds).
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 www.teammd.net.