Protank is NOT a rebuildable. Even if there are many, I was one, who build them.
How long?? Well I guess that depends on when you plan to die. or if the Government bans access to materials.
Look at Fastech, plenty of Rebuildable tanks and drippers for less than $10. I suggest a Kayfun to start or Orchid. Kayfun for single coil and the orchid for dual.
But it really comes down to the style and type of Vape you are after. And the device you are driving the atomizer with.
ROFL. Protank head is one of the easiest rebuilds. 30 or 32awg wire, 1/16th inch drill bit, little bit of cotton, pair of tweezers/needle nose pliers, just a couple press fittings and a rubber/silicon insulator. 5 minute rebuild and way outperforms a factory head. The Protank3/Aerotank heads are a bit trickier but manageable. Just have to know what you are doing.
@OP
Eventually rebuilding the protank heads, the rubber/silicon grommets that insulate the positive and negative leads from each other do eventually tear, get brittle and other such wear and tear. Lightning Vapes carries these in stock, so are readily availabe.
However, you might look into an actual RTA, bit easier to manage, and more liquid capacity, especially for out and about, Kayfun Lite, Kayfun Lite Plus V2, Russian 91%, even a Taifun GT V1 is better than the Protank and rebuilding them all the time.