Buy a cheap beginner bass. Chance are, he'll loose interest and you'll end up trying to sell it on CL. Your son is the investment, not the material goods you drown him in. Give him the experience and forget about whether you will make a return on it.
I agree that HE is the investment. But if I can afford to easily buy him something of quality, I believe that he will stay with it longer. My dad wasn't able to buy me good stuff when I was growing up. I got a VERY cheap acoustic guitar and tried the best I could but it would stay in tune, hard to press the strings (for a 8 year old at the time), etc so going cheap drove me away from playing those many years ago. If I give him something really good, I think he can appreciate it and will come to love the opportunity.
The profit was only a tangential remark, not the primary focus of this effort and it was only IF I found something of value. I too am just now learning about basses and the value of some of these quality instruments. As a hobby I buy and sell stuff from high end computers and Home Theater electronics (like Crestron, AMX, etc) to collectible golf clubs so this could simply become an extension of those other efforts in the future. You never know. For now, I am simply trying to buy him something he will cherish for years.
