Well it really depends on the pick ups itself. You can get major brands like Duncan, Marzio and Fender.They range from 90 to 120 first hand. The installation is straight forward. YOu need some tools though. Solder iron, solder, screw driver and cutter.
Open up the guitar and make mental notes of which wire goes where especially the switch. Unsolder one pickup and replace it with the new one. Do this one at a time so that you do not cock up the wiring.
When you are done, do not screw in the pick guard.You need to double check your wiring. Plug in your guitar to the amp. Take a metallic object such as a screw driver and tap the pick ups one at a time. A "thud" sound should be heard.Move the selector switch and tap the corresponding pick up/pickups. If its all good,screw the pick guard on. Re-string and calibrate the height of the pickups to your string height.