DSS wrote:
I need to write an Excel function that returns best price of a government bond.

You might need to make a distinction between US and Canadian bonds, for
example. See http://www.fin.gc.ca/invest/bondprice-e.html .

The actual handwritten formula is quite complicated, impossible to display
here, and the input values for this formula are-----------------
Accrued days, Number of coupon period days, Days from settlement to next
coupon date, coupon periods per year, number coupon periods between
settlement & redemption, annual yield, discount rate.

As I understand it, PV() should be sufficient, given correct inputs.
But there is also the PRICE() function, which might be more applicable
to the inputs. Use Excel Help to find other bond-related functions.