Can be done fairly easily, but at a pretty good price tag. Need a starter ($40-$75) depending on type needed, battery ($40-$75) depending on type, switch ($10-$25) depending on type, wiring harness ($5-$25) depending on who makes it for you, mountings for switch, battery, harness etc. ($5+$10), and labor (0-$100) depending on who will do the work for you. Low end if you do the work yourself and you use the cheapest parts you can find and you do the labor $150. High end if you need expensive parts and you pay some one to do it $250-$300.
#3
StarTech
Don't forget might need a flywheel if yours don't have the ring gear.