That would be the site, thanks PBO! They sell some pretty nasty stuff, not cheap but you should be able to do your whole conversion from that site (maybe source your lipos from HC though).

Another good site is tnscooters.com.
I was having trouble viewing the pics, but from what I could see this is what I would do.
If it were me with a budget of 200 bucks. I would pick up one of the 48V 40 to 100A controllers for about 45 bucks, yk42-4. run 4 of the 6S 5000 packs with 2 in parallel for 44.4 volts. You will have lvc kick in a bit sooner, but your cells will be safe.
You can replace the battery you have with just lipo and you will see a good speed increase, but at the end of the day those controllers limit your current so you dont get as good of a performance as you would like. From what I could see it was a 24V motor and controller.
I have a modded electric scooter Schwinn S750 with that controller and the 36V 1000W 1020 motor with 14S lipo at 10AH and its pretty crazy.