My friend and I did this last summer. Including airfare to Dublin from Boston excluding u2 shows, we paid a little more than $1000 each. We stayed in hostels, although it turns out the Holiday Inn would have only been like $30 cheaper a day (because we got private rooms w/ private bath at the hostels). But, don't stay in hostels. No, no.
So figure on hotel being around $70 a day. Food/Drinks about $100 for a couple (some days you'll eat/drink less and others more).
Getting around the cities is cheap enough, probably $20 per day if you taxi it.
Site seeing, I'd say reckon on each event costing around $10 pp(like site-seeing the Gaol in Dublin, or the Guinness Brewery).
Getting from Dublin to Scotland can be inexpensive
if you:
a) book in advance
b) book on
Ryan Air or a comporable inexpensive airline
c) do not have an excess of luggage!! My friend and I had heavy suitcases and had to pay like $60 extra to fly from Dub to England.
But I'd estimate getting from Dub to Scotland for $200 for a couple, if you can do it well/bargain prices. (Ferries might be cheaper, just take longer travel time.)
Getting around
in Scotland can't be too expensive. But I'm not sure about that.
Oh and seeing U2. $55 per person per show (based on Elevation-prices & inflation).
So-- olive's cash estimation for:
2 U2 shows
+ 10 days in Dublin/Scotland
+ Food
+ Travel in & between the countries
____________________________
$2400 for two people
I think.