Oh, so no just RAM expansion, but you mean another ACA (1221 - the one with unblocking features)... 80 EUR, sorry, that makes whole thing twice as expensive as single ACA500 only for a sake of more RAM (otherwise ACA500 is just enough to have) and whole expansion gets too big (for my personal preferention).
I guess you overestimate (maybe for a reason
) cost and trouble of soldering one or two smd RAM chips (5 mins of work, soldering smd is no rocket science in 2015) to ACA500 which together with firmware upgrade would do 4 MB which would be fine for most Amiga 500 users, I guess.
Finding someone to solder SMD is no big deal, but... I guess it's more of a marketing that ACA500 was reduced to 2 MB in first place. No offence, while you obviously produce and offer good stuff, it's right of a potential customer to comment on it anyway
I'd be more than happy though to buy "official" 4MB FAST RAM (chips) upgrade (+firmware) for ACA500 at reasonable price if it ever happens (warranty is expiring in time anyway). For both cost and cosmetic purposes - not to make big A500 even bigger