I need to get more batteries and chargers, as we only have 2 batteries and a dual charger for five 250u's.

I've just been shopping around at B&H to get some ideas, and this looks like the best option (?)

2 batteries/charger/cable for $1626.50

I've seen aftermarket/knockoff chargers for $150, but I'm guessing they can't act as an AC power supply if necessary?

Since I'm a firm believer in AB batteries and chargers I'd go for the package myself. When I used fullsized cameras I used Dionic90s with the 2702 4 position intellicharger which could also be used as a power supply and frankly I loved the setup. AB stuff is a bit higher priced than a lot of stuff out there BUT I can say I never had a single worry about their gear. Plus their customer service is outstanding. I blew a a capaciter in the charger (luckily I had a Titan60 charger laying around doing nothing to earn it's keep at the time) and from the time I sent the 2702 out to them for repair and the time I got it back was 7 days.
IMO the AB gear is tops. BTW, I don't work for them and since I don't use full sized gear anymore I don't have any of thier stuff anymore but I still swear by it.

Thanks, Don.

I'm usually pretty skeptical about aftermarket products, but sometimes you get lucky. For something as important as batteries and power supply, I'm probably best off not taking any chances.

Your other option is IDX - I work with their stuff and never had any problems.

I've used Globalmediapro batteries and they are cheap and exceptional. I got 4 hours of each battery. Only downside being they are light, and might not give the counteweight balance the AB or IDX does.