Hi there, Mbikes!
IMHO you have several options available:
1) Monitor your local Craigslist for a
quality used MTB. This option will usually require patience. This is most probably your best choice!
2) You can slightly increase your budget. Go to a Schwinn dealership and get a Schwinn Frontier MTB.
3) You can slightly increase your budget. Go to Jamis dealership and get a Trail XR MTB.
4) You can buy the Nashbar AT-1 MTB online from Nashbar. The bike arrives 90% assembled already.
The Nashbar AT-1 MTB ~ $200
www.nashbar.com/bikes/Product_10053_10052_172828_-1__202617
^ This is better than Walmart or a big box store! ^
If you have trouble assembling your bike, just watch the video below:
www.bikesdirect.com/instructionhelp.htm
5) You can wait until you've save enough cash to buy the Giant Boulder from a Giant bicycle dealership. The Giant Boulder is made of chromoly steel. If kept dry, it will last for an entire lifetime. You will be able to upgrade or change the components on this bike for the rest of your life. It will be your last purchase ever of a MTB. If the suspended fork should ever fail, your can get a much better fork and place it onto this quality frame. You could do the same for any of its worn components, throughout your possession of this MTB. The Boulder frame is extremely durable. More durable than most other MTB frames. It will be a worthwhile investment of both time and money, just to wait and purchase this MTB in particular.
I think this is a great idea! Especially if you belong to a co-op...
The Giant Boulder ~ $360
www.giant-bicycles.com/en-us/bikes/model/boulder/9043/48922/
6) You can purchase a MTB frame online this summer, and your son can join a bicycle co-op. There, he can find various parts or components of bikes, that will fit his new MTB frame. Any part not present at the co-op will have to be purchased independently. It could very well take the entire summer or even longer, if you can't locate all of your needed components at the co-op or can't afford to purchase needed components elsewhere. However, in the long run, at the end of the day, your son will have learned how to service his own bike and others, as well. He would have acquired the skills of a blossoming bicycle mechanic.
Before you buy a frame online, check with the bicycle co-op first. They may have a nice frame waiting for one of their members, already.
http://store.somafab.com/mtbframes.html
The Nashbar Double-Butted Aluminum MTB Frame ~ $100
www.nashbar.com/bikes/Product_10053_10052_173009_-1_202337
The Fuji Tahoe 29 SL MTB Frame ~ $210
www.nashbar.com/bikes/Product_10053_10052_527351_-1__202337
7) Maybe you don't have the time or patience to wait for a quality MTB to appear on your local Craigslist. Maybe you don't want to visit any LBS, like Schwinn and Jamis dealerships, to find bargains on quality new or used MTN bikes. Maybe there is no interest in bicycle co-ops. Maybe the whole idea about a chromoly framed MTB sounds empty to you. Perhaps you just want a MTB within your price range right now and you don't want to bother with any online merchants. You just want your MTB and you want it right now, as long as it's within your budget. No matter what!
Well in that case, you're gonna have to possibly suffer the experience of buying a MTB from a big box store, where all of your bicycle components are practically guaranteed to be of the lowest quality. Chances are, the parts or components of the MTB will be improperly installed, and pose a risk to your son's personal safety. Therefore, if you should decide to go the route of a big box store like Walmart, you should have a professional mechanic checkout the build of the bike, in order to make certain that the build or installation of parts was done proficiently. That will cost extra, unfortunately.
For this venture, you'd best belong to a co-op too!
Popular cheap big box store hard tail MTN bikes include:
The Schwinn Aluminum Comp-The Mongoose Deception- The Mongoose Snarl
Don't ever buy a dual suspension or full suspension MTB of any kind from a big box store!