Here's a not so cheapo:
http://www.ebay.ca/itm/Professional-30A-12-24V-Solar-Charge-Controller-Fully-Adjustable-/291170233312?pt=LH_DefaultDomain_0&hash=item43cb192be0But I have no idea what to make of,
"The solar charge controller status such as "Fast charging" , "Equal charging", "Boost charging", "Float charging" and "No Charging" indicate which stage of charging is in process. After a certain period of time of operation in the "Boost" and "Equal " charging modes, the Float" charge mode is resumed."
OR
" Note: The fast charge voltage is fixed at 14.0V/28.0V, users do not have their own set".
...After a certain period of time? 10 minutes? 2 hours?
...And why is "fast" mode fixed, while all the others are adjustable?