Which ones are easier to install? Which ones are cheaper?

 

The installs are the same if not the elkas being a little easier do to being a true dual rate system and having 2 springs. The Elka's are not cheaper though. I love mine.
Do a search on Elka and read my "therock" posts. Also do "Progressive Springs". Just about everything has ben said on both these spring systems.

 

I put the progressive springs on my P700, and LOVE them!! It removed the push and nose dive in the P700 completely. I didn't notice any harsher ride or problems with long rides at all. I installed mine in about 2hrs start to finish, that includes making a piece to compress the springs in my hydraulic press and remove the c-clip.

The Progressive springs are WAY cheaper then the Elka! I got mine on Ebay brand new to my door for $110.