Cap rate and cash-on-cash (COC) are two very different things. Cap rate is based on market trends and the NOI taking out the financing variables, while your COC is based on the operations of the property along with the financing terms you are able to achieve.
Figure out a value of the asset based on the following: the $7,200 of gross rents is monthly? If so, you're looking at $86,400 per year in gross potential income. From there you'll want to add whatever other income you might have from laundry, storage, etc, and then you'll want to back out all your expenses - vacancy, bad debt, taxes, insurance, utilities, prop management, professional fees, general and administrative, advertising, etc. As others have mentioned a reasonable purchase price is based on the market trends - comps and cap rates for similarly sized product in your market. Last I saw for primary/secondary markets you can expect a cap rate sub 8% - again this will be highly dependent on what is actually happening in your market so do some DD here. So, take your effective gross income minus your expenses to get your NOI - use a T12 here. Then use the market cap rate for similar product and you'll reach a potential value. You can even use a cap rate range; like 7% - 7.5% to see where that puts you. Compare this number to comps on a per unit basis to see if anything looks funky - higher rents versus comparables will give you a higher per unit cost so be sure to double check.
Next, run some analysis based on your newly found estimated value and some financing assumptions - you can use the Bigger Pockets calculator for this or run your own model. See what numbers make sense and you'll reach a reasonable offer. Hope that helps.