Yes a vet gelds a horse or should. I know there are still some 'people'
who do it themselves but that is wrong & avoid that at all costs.
The costs will vary depending on your location or if there are any complications.
Did you get a new horse?
Yeah the costs vary greatly depending on the age of the horse, your location and even can vary from vet to vet. When we got Kid gelded in March one vet (the regular vet for the farm he was boarded at) required him to come to the clinic and the cost would be $300-500. Our regular vet would do it at the farm and the quote was $200-300 and ended up being around $200 AFTER a recheck and round of antibiotics when he got infected.