Fair point. The thing is, I'm not really concerned with "perverse incentives" because, to be honest, I don't want to encourage people to work. I think people should work if they want to, but I don't subscribe to the visions of society wherein employment should be the ultimate goal of an individual. The current economic system makes it perfectly possible to guarantee everyone a comfortable existence even if a significant share of the workforce doesn't participate, provided sufficient redistribution.
Still, if my estimate was too conservative, let's triple it: still less than 5% of the budget. It would require a few changes to pay for it, but would still be far from having a prohibitive cost.