My company needs a 5hp AC drive for our pump, what's it cost price?

Different AC drive and different brands have different price, it's almost not the same, for pump application it's normal to buy a related drive, it's cheaper than the special function AC drives like vector control. the other factor is what's the brand you would like, like ABB, Siemens, Danfoss etc they are famous and have good quality, it may cost much than other brands.

Honestly for a 5HP AC drive it's almost the same among different brands about the function and quality, I think it maybe more practical for you to buy a second level brands drive with cheap price, the pump application is normal and used widely.

Hey

If your pump is working 7/24 at full load, it's no need to buy a AC drive.

I do suppose you want to control the pump with a pressure sensor to get constant pressure, then it's necessary to apply a drive for it.
I personally suggest you buy a Siemens or ABB drive, it's easy to get after-sales service all around the world.