I'd say it depends on what your son wants to do with them - if he just enjoys collecting and maybe playing the game itself, it's definitely worth it. With my cousin it was like that, he started without thinking about appreciation at all, and now he has a collection that just brings him joy - and on the side, some individual cards have actually gained value. The problem comes more when you're speculating on quick profits from the start, then you easily lose track and spend too much.
I'd ask your son what he's most into - collecting only certain series, playing with friends, or just having the nice cards? Depending on that, you can get into it way cheaper, and it's not just standard boosters either - there are also newer sets that are cheaper than the old stuff.