PEP ZPS will run you $2200. If you want to put ZPS on the rear, you must get all new ZPS shocks for the front.
If you want to cut corners using PEP, they'll reuse your rear damper and install a dual spring for about $300 less. For about $800 less, they'll reuse your rear damper and install a single spring. They told me the single spring choice isn't nearly as good as the dual spring rear.
Personally, I don't think reusing the rear damper for the $300 savings is worth it. I believe with PEP's own damper, you get more suspension travel and economically, you'll always have the original rear shock to put back on the ATV when you eventually sell it. If you opt to rework the existing damper, that expense and effort will be 100% wasted fi you trade in your ATV for a new one in a couple of years and you'll have to start all over again.