I have the Lacrosse charger (BC 700) and Eneloop batteries and I couldn't be happier as well. The Lacrosse charger is much easier to use than you think.
I am actually using a very cheap set of regular nimh batteries with my 360 controllers and honestly I get like 30-45 hours out of the controller, it takes me several weeks to play that much, certainly much more than a couple days of casual use. So by that you should be able to put any cheap rechargable batteries you have laying around into the 360 controller and have it last for a very long time.
I think the trick to rechargable batteries is not the batteries but the charger, if you get a good charger like the LaCrosse charger and use it properly and use it to refresh your old batteries then you should be in good shape unless the refresh doesn't work, then its time to buy new batteries.
The only problem with Eneloop batteries is they don't sell them in stores around where I live. You can of course, get them from Amazon. We don't have a Costco, whom does sell eneloop batteries but useless for me as they are not in my area. I go to Sam's club but they only sell Energizer rechargable batteries and I will NEVER buy those again, WORST batteries ever made!
I like eneloops so much that I invested in that glitter 8 pack that is available on Amazon.
If you are desperate and can't find Eneloops the best rechargables sold in most stores are the Ray O Vac Platinum, I think they are a Kiwi green color in a white package. Don't get the other packages of Ray O Vac as they aren't good.
The Duracell's sold in stores aren't good either, I have no idea what happened to Duracell's line of pre-charged batteries (Duracell pre charged batteries are just rebranded eneloops, look for the ones with the white tops) but they seem to have disappeared from all stores in my area. They only seem to have regular NiMh now, which don't hold a charge for very long.
If you want some really cheap batteries Big Lots has some Polaroid rechargable batteries for $6 a pack, they are NOT eneloops though will not be nearly as good, however if you already have a fancy charger sitting around then they might work for you if you are strapped for cash and can't afford to order some eneloop's from Amazon.