Ok here's some advice. I have the exact bike, the Mongoose Mac, that your considering & I love the bike. The frame is solid and for the price of $180. it just looks nice. As someone mentioned you DO NOT need a sprocket adapter. Frankenstein offered me great advice to simply drill holes in the stock sprocket you'll get with your kit. When you remove the back disc brake rotor just align that with your sprocket and mark your holes and drill. You'll attach that right to your hub and it's a lot better then any adapter. And since your getting rid of your back brake just add a back caliper and you'll be good to go. I personally WOULD NOT go wth the cheapest 66cc kit you can find on eBay or whatever. I was also searching for the least expensive set up but there's a 1,000,000 warnings from motorbikers who will strongly suggest you spend a bit more and get a quality set up. I went with the Grubee Skyhawk, got it on sale but you can readily find a kit for $150-200. With any kit there's always room for upgrades, for me I'm constantly trying to figure out how to improve performance. With mostly any kit it's suggested you get a quality chain tensioner & depending on your bike a sprocket adapter. If you go for the cheapest kit then I'd definitely get quality hardware, 8.8 bolts. Prior to having the Mongoose Mac I had a Schwinn beach cruiser & I got tired of it for a lot of reasons. So here's a list of my upgrades, Chain Tensioner ($30), Hub Adapter ($40), CNC Head ($40), Expansion Chamber ($55), Carb ($25) Thumb Throttle (I do not recommend this so I bought a different one), Throttle ($15.), New Spark Plug ($5.) Lights ($60) and I purchased a couple of things to prevent flats ($30). I got all of that & now I'm trying to figure out how to port my cylinder, it's an addictive hobby. For you I think if you spend $180 for the bike, $150-175 for the Grubee kit, $25 for the chain tensioner & $5 for a spark plug you'll be going about 25-30 mph max in no time and you'll be worry free. If you do get that frame be sure to post pics. Wow that was a lot I wrote, now I'm going to sleep.
