Reddit mentions of The Flash Vol. 4: Reverse (The New 52)

For those of you interested, Manapul and Buccaletto (the creative team behind this page) did an excellent arc for The Flash from New 52 #1 through #29. These are collected in Vol. 1, Vol. 2, Vol 3, Vol 4, and Vol 5. I highly recommend reading them if you're interested in the comics, as they are a great introduction to the character of Barry Allen.

This is gonna be much harder, as the individual issues are pretty valuable. 1-30 would go for around £90 if you bought it that way.

What you can do is buy things called trades, which are collections of around 5-6 issues each. I'd probably go with Amazon for these. So, for example:

http://www.amazon.co.uk/The-Flash-Volume-Move-Forward/dp/1401235549/ref=sr_1_1?ie=UTF8&qid=1413383034&sr=8-1&keywords=flash

http://www.amazon.co.uk/Flash-Volume-Rogues-Revolution-Numbered/dp/1401242731/ref=sr_1_7?ie=UTF8&qid=1413383034&sr=8-7&keywords=flash

http://www.amazon.co.uk/The-Flash-Volume-Gorilla-Warfare/dp/1401247121/ref=sr_1_5?ie=UTF8&qid=1413383034&sr=8-5&keywords=flash

http://www.amazon.co.uk/The-Flash-Volume-Reverse-New/dp/140124713X/ref=sr_1_15?ie=UTF8&qid=1413383034&sr=8-15&keywords=flash

These books in total collect issues 1-24. You'll likely be able to find them cheaper on the other sites I recommended, especially eBay.