The "problem" with molle rigs is that money adds up quickly when considering pouches.
With that being said, I had a TT mini mav for a while and I really liked it, I ran it on either a simple triple M4 pouch or a double + a 4x3 GP.
The only "downside", if we can call it that way, is that it's not swift clip compatible so you can't strap it to a plate carrier, if that's your jam.
Failing that, the Helikon TMR, it's €100 but it's very well made, even though it has fixed pouches it takes M4 and Ak mags just fine. A subgun insert can be jerry rigged (thanks to @SgtTalbert's idea), but tough cookies if you run AR-10/7.62x51 style guns).
If scalability (and future proofness) is a requirement, then you can't go wrong with the Ammo Hub from @TheFull9, it's not the cheapest solution but it's very well made and it'll take any insert/pouch you want. Doesn't come with a harness so you'll have to pick your own too.