I’m not very familiar with the lower end of index printers. Bambu does exist and seems to work well, but have no support for multimaterial flexibles, and I’m not a fan of the closed nature of their printers.
There are a few other solutions for single toolhead mmus, such as the prusa mmus and the ercf, but those have the problems you mentioned as well.
The only multi toolhead solutions I know of are on the high to very high end (Prusa XL, Voron Phoenix, and there are some projects for toolchangers and idex for the Voron 2.4).
A note on the Mercury wash station: despite being sold in a bundle with the Saturn 4 ultra, the build plate of the Saturn 4 series does not fit in the tub, so I would not recommend it for those printers.