You may already be tracking this but the price to get it converted will likely be close to the price of just buying another PSA rifle. I don't know how a professional will do it but if I was doing it on my own, it would involve grinding off the old rivets and removing the pistol rear trunnion, sourcing a folding rear trunnion and associated stock (not all folding stocks use the same rear trunnion), filling the existing holes in the receiver for the old rivets, drilling new holes for new rivets (rivet locations on the folding stock trunnion are different), rivet in the new trunnion, then refinish the whole gun because I don't see how they will swap it without damaging the existing finish in some way.
I'm just a garage gunsmith. It'd take me a day. A pro's time alone is likely almost worth about what you paid for the PSA AKP