Its best to have the same tyres all round, however, as long as the front two tyres are the same and the rear two are the same its not the end of the world. (Change the back two, then change the front two to match the back when required)
I have had Scoobies for the last 8 years and I always use TOYO's (Proxes T1R), find them to be an excellent all round tyre.
Cheapest place I know of is Davey Stuarts Garage in Dumbarton, next to Dumbarton Common & Central Train Station.
01389 764449| Dumbarton Service Station, Townend Road, Dumbarton, Dunbartonshire G82 2RB
Phone and ask to speak to Davey, should get a good deal.
Good thing to do is get your choice and size of tyre, phone round different companies for prices, you will see a great fluctuation in price.
Paul