When should I buy DayZ?

Never.

since ARMA II complete edition was on sale I grabbed that one. I really dont think he will mind playing with the mod version.
Thanks for the suggestions!

Who cares about DAYZ?
Get ARMA 3 instead and download Epoch mod and/or Jurassic mod/Raptor mod.

It doesn't worth to buy it in its current state. I bought it and I regret it. Get Arma 3 instead and play some mods like Life mods or Battle Royale, it's mad fun.

When it's done?

The original DayZ ARMA II Operation Arrowhead mod is much better than the standalone still; Vehicles, base building, more weapon choices, etc... I'm with the crowd that has buyers regret for DayZ Standalone, it hasn't gone the direction veteran DayZ players had hoped for and has received very few small updates, most of which don't solve the problems that plague the game.

50% won't happen as a lot of people have said, but it might go to 25% at the most but even 10% is the lowest they been ever I believe

Having played it almost 70 hours ...

AVOID IT! It's almost a scam. The updates ARE SO FUCKING SLOW. I feel, honestly, kind of betrayed. YOU CANNOT EVEN hunt yet, what the fuck Bohemia Interactive are doing? The DayZ-mod looks better, runs better and IS BETTER IN EVERY WAY. Get the mod! Arma 2 complete is 80% of!

Like everyone already said, get the mod, not the standalone. First because it's much more worth it (you get DayZ + Arma), and the standalone is one, big, bugged borefest of walking/dying simulator (fanboys are free to rage at my post at this point).
Seriously, I know I should be happy to own that famous popular alpha game, but believe me, it's currently NOT a game. Eventually? It might have some potential. But right now, don't even bother wasting your money on the standalone when the original mod is way better (or so I've heard).

Don't buy it, don't! The game is unplayable the most game breaking bug where zombies glitch trough walls & doors has been in the game for about a year now & all they say is they will fix it at a later time. It's like the developers have abandoned the game & once in a while they come back to grab some more cash, then they'll put out a small patch. This developer is on my blacklist, I'll never buy their games again. Also in the videos it looks fun but really it isn't, biggest regret I ever had buying a game.

Afaik it's not being developed anymore because that rocket wanker was too bored by it (or he just didn't have the skills to do it properly) nad it's such a crappy bugfest it's not worth the money. I'd rather wait for someone to make an actual game in that fashion.

Dont Buy Dayz just wait for H1Z1.

buy bad rats, is bether than DayZ ..

If you really want it, wait for a discount of 75% off or more. Also keep joining giveaways. you might win it and save the money.

DayZ is a awesome game if you are into surviving and player interaction, don't waste your money if you want DayZ for fast pace PVP.

The haters above are angry because you can't insta PVP like in the dayz mod were you spawn with weapons or you find cars and weapons all over the map.
Dayz mod is more arcade'ish, you're low on blood? Use a bloodbag and you're at 100% two seconds later, while in Dayz SA you need to eat, drink and wait for 15-30 minues to become healty again.

Wait until Q2 next year, by that time the game will have the new renderer in, vehicles, more polished content and maybe the new zombies.

never.