The Enginer kit is currently $1,495 for the 2kwh system. $2,295 for the 4 kwh system. The site says these are sale prices that are only godd through Dec 31 or until suplies last. Usually the 2kwh is $1,995 and the 4kwh $3,495.
Enginer | Prius Plugin PHEV Conversion Kit with Lithium-Ion | Hybrid
Installation is generally an additional $500 if you have an installer put it in, but if you have confidence and good skills you may opt to tackle it yourself.