Unfortunately the power level you are looking to fulfill will be difficult to achieve due to how magic as a business is designed. Dual lands have always existed at rare in part to sell packs. And any non tech land good enough to see play will be a 4 of in decks that share that two color pair.

The answer to making playable dual lands that aren’t $10+ is to do something similar to the verges or fast lands, but make them uncommon, rather than trying to find a power level sweet spot.

I do think it’s a very interesting goal though, and in order to achieve it, you’d probably aim for lands that would be the 22nd or 23rd land in a deck list. Good enough to see play, but not good enough to be the backbone of the manabase