question for a tax preparer
You are correct in thinking that it is self employment income. You should report this income on a schedule C or a C-EZ. You will be able to list your cash income and the expenses related to the cash income. For example, if you had to buy cleaning supplies, you can deduct that from your cash income on the C or C-EZ. For more info about what you can deduct, see this IRS publication: http://www.irs.gov/pub/irs-pdf/p334.pdf
Note that you might have to pay self employment taxes of 15.3% on your business profit in addition to regular income tax.
If you're uncomfortable preparing a Sch C or C-EZ, you might be able to go to a Volunteer Income Tax Assistance site where they can help prepare your return. You can find the nearest VITA site here: http://irs.treasury.gov/freetaxprep/