I would say pass on this. Even if it were free, it might be no bargain, as even as a DIY project you could find yourself putting $100 or more worth of work into it, plus your time. After all, you aren't talking about bombing around the neighborhood with your 5 year old. You are talking about doing some decently serious riding. You wouldn't play American football in a leather helmet, so why are you contemplating club rides on a bike that is really more of a bike shaped toy?

Cycling doesn't have to be ridiculously expensive, but it isn't dirt cheap, either. I just bought myself a new pair of cycling shorts, on sale, and 4 new water bottles. It cost me $68. Did I absolutely need the new shorts? Probably not, but on longer rides, comfortable bike shorts make the ride more enjoyable. A set of clipless pedals will run you at least $40, as will a set of tires and tubes. Decent shoes will cost more than $40.

And if shorts, shoes, and pedals make riding more enjoyable, a better bike will reap large benefits. You don't need the latest carbon fiber racing bike, but you shouldn't settle for a cheap Huffy, either. If it were me or my wife, son or nephew, I would say to hold out for something slightly better. Maybe an old Peugeot, Raleigh, Miyata, Schwinn Super Le Tour, Trek, or Giant. Alternately, look for a better quality 90s or early 2000s era hybrid. Not ideal road bikes, but much better than that Huffy.