There are many options for encoders once you decide to spend some money. Is the US Digital The best buy. What CPR would most teams want to use. I'll Throw this out for thought. CUI makes the AMT102 and AMT103 encoders. Digikey link hear.
http://www.digikey.com/PTM/PTMPartLi...ng=en&ptm=5586
Now they are meant to mount on a shaft like the current US Digital that Andy Mark sells. The big difference is that they can be set to many different CPR up to 1024. You can turn these into a sealed unit with shaft. We made a base plate out of polycarb in the shape of the AMT102 base. In the polycarb base we mounted 2 precision ball bearings for a 1/4" stainless shaft. The programmers played with them last fall and they seamed to work well. We have not used them on a robot or really given them a test. Other teams have posted that they worked well. Could a run of base plates be done to add shaft capability to them? Then all that is needed is some shaft and bearing. I believe the bearing were about 5$ apiece. Is this an option?