€305 for some lad to spin out to your house and put 2 bait boxes down.... That's criminal, especially since he only managed to place 2 to cover an entire house.
Also you're right - If he had any interest in doing his job properly he could have checked the house and attic for droppings/signs of nesting and targeted his efforts properly, it speaks volumes that he couldn't haul his backside into the attic for 5 minutes work.
The traditional wooden mouse traps below are just 99 cent each and they work brilliantly - You definitely will not need 300+ of them anyhow....
Wooden mouse trap Raised platform Easy disposal
www.lenehans.ie
Tesco, most hardware shops, convenience stores etc all stock them (ie a version of in above link)
When we had this same issue OP it was very quickly solved by buying around 10 of these, putting them in key locations around the house and baiting them for a couple of days.
I found the knack to it all was to use a bit of cheap chocolate as bait ---> Put them in place first ----> set the trap but then use a ruler (or anything that's not your fingers) to very carefully prime the spring retention mechanism so its totally on the point of snapping. By this I mean that theres just the barest sliver of metal keeping the trap from going off... This takes a little practice!
OP also if you can mange to get over the mental side of this issue it would be a big help - Mice are very commonly kept by kids as pets, they're totally harmless, kinda cute in their own way and just an annoyance that will pass very soon - The very worst there'ye going to do to you is nibble at your possessions and be a minor inconvenience.
Finally don't get a bloody cat - Kill the mice using traps, you've enough to be getting on with without having to go out and buy a cat before paying for: cat beds, litter tray, neutering, feeding, constant clean ups (smell + cat hair everywhere), pay ongoing veterinary bills, cattery costs etc.
PS Just to add that this commonly happens when the weather get colder - They move indoors. Also if your neighbours don't take action then there's a fair chance you'll continue to see mice until they do.