The purchase price of the piano is $3620.05866.
To determine the purchase price of the piano, we can use the present value formula for an annuity. The formula is given by:

Here,
PMT represents the monthly payment, which is $124,r is the monthly interest rate expressed as a decimal, calculated as 9%/12=0.0075
n is the total number of payments, given by 2.5×12,D denotes the down payment, which is $300.
Plugging these values into the formula, we get:

After performing the calculations, the result is approximately $3620.05866. Therefore, the purchase price of the piano is approximately $3620.06 when rounded to the nearest cent.