Here's the very simple problem: you're budgeting as if the bands will recoup no money. If the band's prospects of making any money are that low then why on earth would they be playing 2-400 capacity venues and blowing 8k on a single? Who operates like this? Who stays in hotels when they have no money? Sleep on floors! And you didn't include the cost of getting absolutely fucking rat arsed every single night.
Right, back to proper discussion...
€30 x 6 people x 3 nights accom = €540
€100 petrol x 2 cars = €200
Food €15 a day x 4 days on the road x 6 people = €360
Venue booking
Crawdaddy = €350
Cypress Ave = €200
Spirit Store = €150
Roisin Dubh = €200
When you take into account all the costs, it takes a good bit of cash to get jobless teenagers around Ireland for a few days.
I can't see how you'd get around the four counties for any less and the food budget is miniscule. You could do supports instead of headline gigs but this particular band saw this as less suitable for launching a single. It doesn't make too much odds seeing as you can break even on the door take at a headliner or play a support for free.