Sure there's a 4-valve version. Really, you need to come up with a budget because a full blown honda Nice motor will run you close to 4k I'd think. If you don't have a motor to start with and money burning a hole in your pocket, i'd just suggest you buy it complete from TJR. If you want to do it yourself, buy a complete bottome end from asian concept thai and then get the rest of it yourself.
A 127cc with a +r will be plenty capable for most people and you can score it for a total of about 2k. Add a TJR crank and you're in for about 3k with other necessary mods.
You can build a chinese motor that makes as much or more power, but the longevity and reliability could be in question. While I have a GPX177V2 motor with over 1200 miles on it, it has never given me any trouble. I suspect my nice motor will be stone reliable since I'm not punching the bore out beyond the capabilities to keep it sealed with gaskets.