Hi Bradley,
I would not recommend using the prevailing cap rate to establish the purchase price. Instead, I would do the following:
1) Establish property performance during your anticipated hold period including a projection of income, expenses, and cap ex to establish a series of annual cash flows. Keep in mind that nailing rent projections is critical. Rental income disproportionately drives property performance.
2) Establish a sale value at the end of the hold period and incorporate these sales proceeds into the cash flow analysis that you developed in #1
3) Establish values for the "big three" performance metrics that would be acceptable to you given the level of risk that you are assuming with the acquisition: cash-on-cash return(CoC), IRR, and MOIC (multiple on invested capital)
4) When you have projected the cash flows that that property will produce, and established what returns are acceptable, then you can solve for the purchase price
I hope that this helps.
Good luck with the analysis possible acquisition.