Large scale hexapod robot parts selection

[jameskpolk]

I am attempting to make a large scale hexapod robot, and by large scale I mean that I would like this to have maybe a 3 foot leg length, capable of carrying a large payload. 
This of course results in many other issues, primarily power, and strength of motors.  Most common servos will not be capable of this type of weight.  So it leaves me with a few choices: electric linear/rotary actuators, vacuum/pneumatic actuators, or hydraulic actuators.  So the purpose of this thread is to get some recommendations from the community of the validness of some these selections.

The straight forward choice is electric linear actuators, which are common enough, though generally slow and expensive, with limited control.  I have found http://www.firgelliauto.com/product_info.php?cPath=114&products_id=233, which would probably work, though they are not encoded, so I would have to implement my own rotary encoder of the joints of the hexapod, and they are hella expensive. 

So do you all have any advice?