Easy to do within your budget. I am in Scotland too and the first two weeks in July is the cheapest, before the English schools break up, prices go up considerably afer that, both for flights and accommodation.
I like to use otbeach.com as a starting point I have just priced up a few holidays and there are hundreds coming in well under your budget.
You can look there and then source flights direct with the airline and accomodation directly.
Flying from Newcastle can be cheap during thta two week window too, as it is in England, so local schools have not broken up. Prestwick is generally cheaper than Glasgow airport too.
There don't seem to be many flight deals around atm, I keep an eye open week by week and check the prices with jet2, Ryanair and easyjet.
Unless you are set on Spain do consider other countries, flights to Portugal are usually cheap, and although flights to Turkey are more expensive things are cheaper once you are there, and all inclusive is usually very cheap.
Keep an open mind and don'rt be afraid to leave it until much closer until you leave there are always last minute bargains.
Last year we flew from Edinburgh - usually expensive- to Malta with Ryanair, we are two adults and two teenagers. Flights with Ryanair including baggage cost £650 and accommodation was £480 for two weeks starting the first week in July.
We booked 3 weeks before we left and stayed here in Gozo:
www.gozovillageholidays.com/villaggtasbejha.html
There are plenty of holidys that you could find for £1500.