The company that has the double/triple minute cards is tracfone. Even considering triple min for life, net10 is cheaper. I did a LOT of research and pricing on this and net10 ended up being substantially cheaper than even using triple minutes on tracfone. Either of these is vastly cheaper than the big companies like AT&T, Tmobile, verizon, and the other co's.
If going for the pay as you go, I would find the cheapest phone possible because they are the hardest to text on. You can often find deals on ebay for them, not sure about HSN. You can also buy from the net10 website. Just NEVER buy the min by putting a credit card # into the actual phone. Buy the card at the store or put the min on by using the website ONLY.
Kajeet sells the firefly phone, or they did a year or so ago. They have the BEST parental controls out there. You also might look at the AARP website because many seniors do not want internet on their phones so this is an option on some of the companies that AARP endorses. I looked at phones for my mom because she was having problems finding phones she could use easily (she has wrist issues). You could also google "phones for seniors" to find more than the AARP endorsed ones. I would look at the ones for seniors and then try to find one you could use on a pay as you go network.
I did look at tracfone phones because they are reasonably affordable and n be found at lots of places. Plus they had more no-internet phones that I could find. Even with being more than net10, they are still cheaper than the other pay as you go providers. I found the samsung t101G that is available on amazon for $29.99 and problem at dollar general for about $10. It is a 'candy bar' phone and would be easy to use and problem far better for a kid who cannot stop buying stuff online via his phone. You can go to tracfone.com and search for phones from $10-$10 (click on browse all phones then check the box for the price range. It will show phones in that range and toward the bottom are the phones that won't go online.). I would look at phones first, then on the ones offered in your area because you can always check ebay/amazon for a model not offered in your area.
Hope this helps. If you do want to let him go online, go with kajeet even though it is more expensive. I have a feeling the parental controls would be worth it.