Awesome! I certainly will. Thanks for your help.

Thanks Pablo! Felix’s motors have been paired with the E3 from US Digital. US Digital is very helpful, and they make great encoders.
http://www.usdigital.com/products/encoders/incremental/rotary/kit/E3
Figure out your design constraints before you order. I would call them if you have questions.

For the Robot Stroller kit I use 2 of the Jazzy Select Elite:
http://www.monsterscooterparts.com/left-motor-brake-assembly-jazzy-select-elite.html

Coupled with 2 of the 12 inch tires:
http://www.monsterscooterparts.com/flat-free-drive-wheel-invacare-nutron-tiger-r2-pronto.html

You can find them on ebay used for cheaper, but these are what I use in the kit.

As soon as you move into the wheelchair motors everything gets more expensive. They are so nice and quiet though. Expect to spend between $400 and $1000 for a motor controller, unless you build your own. I tried lesser ones in the beginning and had a very catastrophic event at a presentation. The time I spent on them was wasted time. If your debugging purchased hardware that is faulty it is difficult to learn much and you can waste a ton of time. Since then I moved up and have been extremely happy with Roboteq’s motor controllers:
http://www.roboteq.com/

Wheel encoders are needed as well, I like US Digital. $160 or so depending on configuration
http://www.usdigital.com/

They are a little pricey for hobbyists on a budget, but pay for themselves quickly when you don’t have to waste time debugging a home grown solution. I built my own and tried a couple of different one’s designed for smaller robots. I really like not debugging wheel encoders.
The robot is a package, if you spend hundreds of hours programming, $2k in hardware, you have an investment. If the parts are solid and have a good track record then you will be able to spend more time on the software which is what closes the loop on a solid project.

I highly recommend building your own systems and trying new things, but if you are doing it while you learn robotics do it with smaller tabletop hardware that is much less expensive to fix, debug, replace and repair.