A deceased relative with multiple parcels of land bordering the desert, which we now own and are quite sure he has buried gold in pvc, sources he bought it from saw him throw them in the back of his truck. The 'up to' 3' deep was a guesstimate.
His home was near this area and was sold without searching.
Can a minelab gtx 5000 be rented ?
Or is there also a less expensive model with similar features?
Sounds like a lot of guessing and second-hand info. Not too many people I know of would just "toss" gold into a truck. It also sounds like he didn't want it to be found with a metal detector if he was burying it in PVC.
Do you have any idea if the gold was in the form of ingots or say one-ounce coins? Or was it flakes/dust? Any idea on the quantity? If you don't want to say, I totally understand. Just know that the smaller the target the harder it will be to find. And metal detectors typically "see" individual targets, and don't gain nearly as much on a mass of them, especially if it was gold dust/pickers. -- A great example of this is with gold chains -- they are MUCH harder to detect than say a flat pendant or coin of equal mass.
If buried three-feet deep, like others have said, a good PI machine with a large coil is your best bet. Something less expensive than the Minelab GPX 5000 would be the Garrett ATX, or the Garrett Infinium. I would use the ATX with the large 15x20 coil. If the Infinium, I would use the 10x14 mono coil. As for rentals, I haven't a clue, but maybe someone in here will chime in, or you can contact any dealer and see if they rent.
I'm not sure of how hard the dirt is where you will be at, but most desert dirt can be like pavement, so digging down three feet wouldn't be easy, or fast in that case. Anyone who has dug to that level will quickly attest to how hard it is. Usually, caches are buried around arms length. But since you said the gold was placed in PVC, again, it sounds like he didn't want it to be found. And if that's the case, it could be deep, or it could be masked, by iron junk, etc.
What you will need is experience with whatever machine you go to use, but I wouldn't recommend buying one if you're not very certain that the gold exists, and you have the cash to front it, or are into metal detecting pretty seriously.