Tank here. I don’t think dual spec is the answer. The number of tanks in retail is due to higher threat modifiers (500% iirc), plus you can get whatever gear you want because it’s personal so there’s no incentive to wait as dps, and there are often extra rewards for tanking (gold or pets/mounts).
Two days ago I was in a heroic SP group, and as we were running in I got kicked for a pally tank, despite being kara geared myself, the idea there’s a tank shortage is laughable.
Also, sorry but the idea that 100g is an issue is laughable, you could farm that in a few hours if you wanted to. I make 20-30g 20 minutes eating breakfast before work flying around mining. If you aren’t willing to pay you don’t want to be the other spec bad enough, that’s not the game’s issue.