If good, affordable, off the shelf incubators existed we wouldn't all build our own. If you don't want to build your own you can either buy a commercial unit which won't be very good or will be extremely expensive, or you can pay someone for a custom built (AKA backyard job) one, and even then, be careful.
Even if you have an excellent incubator (which will either be a backyard build or extremely expensive), you'll need to play around with everything to get it working well, unless you manage to fluke it.