First of all, keep in mind that, by the RAW, both Pathfinder and D&D 3.X mandates at least a +1 enhancement bonus on any magic weapon, before any special effects. That means you can't have a "+0" Inspired Rapier: it should at least be +1 already, and Inspired should be put above that.
There is a really quick way to get the cost of the enchantments of any non-fixed cost magic weapon.
First of all, pick up the total enhancement bonus of your weapon. In your case, you have the mandatory basic +1 enhancement bonus, plus the Inspired special ability. Inspired is equivalent to a +1 for effects of cost, so your weapon would cost the same as a +2 weapon when you sum the two up.
Pick up the +2, and square it up. Then, multiply it by 2.
That's the total gold value, in thousands of gold pieces, that the magical effects of your weapon cost.
On you case:
(+1+1)² x 2 => 4 x 2 => 8
So 8 thousand gold pieces, just on the magic enhancements.
Then, you should add up the cost of a masterwork version of the weapon you want (320gp for a Rapier).
That brings us for the grand total of 8.320gp*, for a +1 Inspired Rapier!
If you weapon was a +2 Inspired Rapier, the calculation would be:
(+2[enhancement] +1[Inspired])² x 2 => 9 x 2 => 18
So, it would cost 18.000gp in magical effects alone, plus the cost of the masterwork rapier (320gp), to a grand total of 18.320gp*.
*Taxes and delivery fees not included.