Originally Posted by ShannonM

Bar-end shifters are Good Things. Simple, light, intuitive (built-in gear indicators!), about as reliable as a shovel, and with a friction mode that might only matter once in the whole time you own the bike but will really, really matter on that day. They are less convenient than integrated levers, true, but not by much. I'd certainly consider trying them out. You very well may like them,. many people do. If not, quality bar-end shifters in good shape are easy to sell.

If you go that route, and if the aero bars do have weird levers, brake-only levers are easily available and not expensive. Most current production ones are in the $40-60 range. My favorite is the TRP RRL SR, but they're pretty spendy, 80-100 bucks. Worth it to me... they're the best-feeling brake lever I've ever wrapped a hand around. Used, any Shimano SLR lever from the late 80s onward would be a great choice. I've never heard of anyone who didn't like them, and they made them for decades, so they're everywhere.

Used integrated levers can be a bit of a crapshoot, as they're not rebuildable and internal parts do not exist. The most-common failure mode is an easy fix: the grease gets gummy and they don't shift right, spray lube into the guts and shift back and forth until everything frees up. If that doesn't work, you're usually hosed.
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Hope that's helpful,