Lujo is luxury, but with darse the translation is often broader. Here are two examples from telenovelas.
- Tampoco podemos darnos el lujo de perderlo. We can’t afford to lose him. We can’t afford the luxury of losing him. Here afford does not necessarily refer to money.
- No puedo darme ese lujo. I can’t take that chance. The risk is too great.
As you can see, the best translation often includes the idea of afford, chance or risk. However, afford to buy something is expressed via alcanzar.