Maybe I'm mistaken but I feel like 'will' is an acceptable translation here for 'mau' in addition to 'want'.
As i understand, 'mau' is not just 'want' as in wish to, but implies that you will do it and i often hear 'mau' used the same way 'will' is used in English. The more general want is 'ingin' or 'pengen'.
Well then you'd just say 'Saya bayar makanan saya sekarang', 'I will pay for my food now,' but you'd probably add 'terimah kasih' at the end to stop it sounding awkward. Mau doesn't really mean will, though perhaps it is implied that you will, same as saying that you'd like to pay for your food now, since there's little reason for the restaurant to refuse.
I think if you want to say "I will pay for my food." or "I am paying for my food." you could say "Saya akan bayar makanan saya." However, I am not 100% sure! The translation as requested here, is correct.
Surely I can say , "I want to pay for my food". Seems the translation is a little inflexible.