Like many emerging technologies, electronic gear-shifting systems for bikes are currently at the point where they exist, but they're still quite expensive. For examples, take a look at the offerings from Shimano, Campagnolo and SRAM. That could be about to change, though, with the upcoming introduction of MicroSHIFT's simplified eXCD system for mountain bikes.
Right off the bat, it should be noted that exact pricing for eXCD has yet to be determined. That being said, there's definitely reason to believe that it may be significantly less costly than its competitors.
For starters, instead of utilizing a proprietary battery pack, it's powered by two rechargeable AA lithium batteries. These are located in the handlebar-mounted push-button electronic shifter/controller, and should be good for over six hours of continuous shifting per charge – MicroSHIFT also quotes battery life figures of 6,000 individual shifts, or over 1,000 km (621 miles) of average riding.
The choice of standard 14500-type AA's means that buyers won't be paying for a purpose-built battery pack. Additionally, should users find themselves with dead batteries right before a ride, they can simply buy a new pair at a corner store instead of waiting to recharge. To keep that from being necessary, though, LEDs on the shifter keep users apprised of the current charge level.
The other reason that eXCD may be inexpensive is the fact that unlike most other electronic systems, it is not wireless. Instead of sending shift commands by radio signals, it uses a connection cable that runs directly from the shifter to the capacitor-equipped rear derailleur – the system doesn't include a front derailleur. This hard-wired setup will result in some cable-clutter, but it once again minimizes the amount of electronics that buyers will have to pay for.
Not much else is currently available in the way of specs, apart from the fact that eXCD offers the same gear capacity as a single 35t chainring combined with an 11-42t cassette (a 3.8 gear ratio), along with a one-way clutch on the derailleur to aid in chain retention, and the ability to fine-tune gear settings via the shifter.
A MicroSHIFT rep tells us that the system should be available sometime next year, and that the company will "focus on the mid price level to satisfy the demand from general riders."