Look at the one on the bottom:
HSGI knife and sheath slides inside and you can attach molle pouches to the outside. Google "drop leg panel" and "web gear" or try Blackhawk, Eagle Industries, Tactical Tailor, Spec Ops Tech (not the same as "brand"), Specter to name few. Probably looking at $100 by the time you're done and that doesn't include the sheath. The upside is once you start collecting molle you move it around - turn the above leg panel into a magazine subload, move pouches you might purchase for the above to a belt/pack/etc.
This guy usually has good prices(he's selling the HSGI for $3 less than HSGI), I'm always checking to see what he has on sale: OP Tactical (pretty good list of manufacturers on this page)

Like I mentioned above, starting out in molle is pricey but the upside is if you're buying durable products (not swap meet tacticool knockoffs) it lasts a long time.