Limiting yourself to built in batteries restricts your choices. Otherwise I would say a Solarforce L2P with XM-L module. This will provide a very wide flood and tons of light, in the neighborhood of 400 or so lumens, excellent for lighting up close in areas without creating a blinding hotspot. You can easily get this and 2 18650's plus a budget charger under $60. Plus it being a P60 format light allows it to be upgraded if you don't like the light output, beam shape, or tint.
Plus one advantage to a replaceable battery is the ability to swap out batteries in case it goes dead. Think about it this way. Every time I went to an impromptu party or go on a road trip, there is always one of my friends that whips out their camera only to discover it's dead. Whereas with my camera I can easily just pop in a set of AA batteries and I always have a spare set of those and a car charger. Trying to get a spare charger and spare battery for a specialty item seems like more hassle than going with an affordable light with affordable standardized accessories.