Everyday (no space): Describes something common and unremarkable.
Example: No matter how much she loves me, my mom probably doesn't want to hear about my teeth-brushing and other everyday events.
Every day (with a space): Describes the frequency with which something happens.
Example: I'm always excited to save $1.00 on coffee when I bring my own mug, even though it happens every day.
So when you advertise your $5 Buck Lunch Everyday, I have to wonder if you meant to say it happens each day or if you think it's not a very remarkable deal.
Hugs & kisses,
B