PowerPak is the retroUSB version. That's also the source for the Battle Kid and the 8bit Xmas carts. (The Xmas roms are also freely available from the site.) PowerPak is $135 but looks like it's unavailable at the moment.
I know they're expensive but for the cost of a couple brews, or even just one aftermarket, you will get a ton of mileage out of it. If I bought one today, I'd go with the Everdrive. Still dev supported but either one will work for you.