Should I let my teenager spend all the money he's saved for a controller?

My son slid $70 across the table and asked me to order the controller he'd wanted for months. My first response was, "You should keep at least half."

He's 14 and gets $14 every two weeks for spending as he chooses. He saved five payments without buying the snacks and game extras he usually asks for. The controller costs exactly $70, and we've checked that it works with his console. It isn't a surprise purchase.

I worry he'll dislike having no spending money until the next allowance. He says that was the whole reason he saved: to buy this thing instead of several smaller things. I realised I'd been praising the growing pile without telling him I expected part of it to remain untouched.

Would you let him buy it, ask him to build a separate cushion first, or offer to cover a small part so he doesn't go back to zero? I want to teach something useful about money without changing the rules at the moment his plan succeeds.