I bought mine at the beginning of the year for less than $20, but as I was watching over the summer, I saw the prices drift quite a bit upwards. Presumably this was from a lot more people doing the diff conversions, and I'm guessing perhaps Flux owners as the the truck got popular over the summer, and all the diff issues were coming to light. For a while, a new diff couldn't be had for less than $30 for the most part (least the times I was watching.) I ended up having to order some spare parts from CEN directly as the diffs got too expensive to just order the whole thing.
Now that they are at cheaper levels again, its a good option. I saw CEN does have some
steel* gears as a HD upgrade now, but there is not a cheap way to get them (least that I know of.) The end up being more than the HPIs BP set if you order them from places like TCS.
*WTH.. steel? are the stockers alu or something?