I don't get what you're asking? you can find either type of aio for cheap these days for starters.
Cooler Master Seidons are like sub £50. There are plenty of options I personally avoid refurbs as you never get the full original warranty and hell at the end of the day why was it refurbed in the first place...
New or Never.
amazon sell the h80i for 65 quid.
whether you should get a new case or not really depends on if you want a new one.
what have you got in the rest of your rig?
are you planning on overclocking your cpu?
ide stick with the case you've got then and just get a h80i. they are really good coolers
i take it you saw that on maplins website?
ide recommend af120 fans. ive got ive got 4 of them and have no problems with at all. all running at 5v so really quiet and move a good amount of air
well in that case ide get 2 more sickleflows because having different fans can cause turbulence and messed up air flow due to different cfm ratings etc
but if i get a h80i or zalman lq series would i have to put 2 sickleflow fans in push pull to balance it out
H80i would be a great choice for the i5 3570k at stock, the H100i is overkill unless your considering OC'ing.
My choice H80i with a pair of Corsair SP fans in push/pull.