Up until a few month back undoubtedly the best core drill for your money was the DDM2 at just under £300 but they have stopped selling it. I have a DDM2 and a 3. Both similar guns but the 3 is faster and £150 more expensive. I don't fancy the DDM1 at all.
Over the years i've had 2 Makita's 1 Dewalt 2 Ryobi Industrial's and a Hilti, none of them particularly cheap. They were all junk except the Hilti and are long since binned. At the end of the day if you just drill the odd hole every now and again your std sds will do the job. If you are coring every day the day a decent drill will pay for itself in time saved within 2 weeks.
Btw screw fix wouldn't be a place of choice for power tools. Search around on the net for something to suit your budget. There are lots of vgood online tool shops selling better gear.