I'm currently a player, so i'll throw in my $.02.
The startup cost is insane. Around 300-500 (depending on the army you want to play), just to have a small army, rules, paints, hobby materials, dice, templates, etc. Then there's the time sink, which could be just clipping models and putting them together, leaving them as grey plastic, or taking the hours, days, months, and sometimes (if you're like me) years to paint. After that, there are the rules which, once you get the hang of them are like second nature, but can take some getting used to (there are TONS of 'learn to play' vids out there, I suggest miniwargaming.com)
The reward you get out of all this is an army that is yours. As an example, no one uses my paint job that I know of, no one used the same background for their army as I did for mine, no one has exactly the same army list as I do...etc. There is so much customization potential, you just need to put the time, money, and effort into it.
Another thing to consider is, are there enough players in your area? What kind of community are they; power gamers, relaxed, creative? I have about 2 people I get to play on a regular basis who are great people, but it's getting stale with the small number of players, which is why I'm branching into X-Wing and starting to look at Warmachine.
Has he played 40k? If not, see if there are gamers around willing to let him use an army and try it. Do the same with Warmachine, Infinity, Mercs, Dust, etc. There are a lot of wargames out there, and most are cheaper than 40k. (FLGS will sometimes run demos on these games too if there's interest)
If he really likes the lore, look and feel of 40k, then so be it. Start small, and gradually work up the army (which no one does, believe me). Try Kill Teams, which is a small skirmish version of 40k. (free non-GW rules: http://heralds-of-ruin.blogspot.com/p/kill-team-rules.html)
Those are some ideas to think about. I could honestly write you a book if you'd like with opinions and the like. Good luck!