You have loads of options in terms of wire and posts. A lot depends on what you have already. The most easily removable will be to use plastic posts and polywire. For top quality, Rappa have some great posts and string and all sorts of gadgets and gizmos to make paying it out and reeling it back in easier.
Being a tight-walleted Scot, I have gone as cheap as possible. I bought cosmetic second and 'short' posts (shorts are where the horizontal bit you stand on to push them into the ground is short or absent). The posts are cheap quality and do bend a bit if you pull the string too tight round corners, but they're a bargain at the price. For string I scoured ebay and set up searches, and found a guy selling about 5km of black polywire for peanuts.
In terms of set up, I've found that against hedges or existing fences two strands of wire seems to be enough, but to split a field I need three or four strands.
I also have temporary grazing, but have decided that on my longer term temporary grazing (the bits that come with the house) I'm upgrading to wooden posts and galvanised wire (which came from a post on here).
Whatever you go for, I think it's worth getting it set up properly the first time. I tried to do it too cheap at first, and now it's taking me almost the same amount of time again to move them into another field - so get plenty of gate handles, gate connectors, lead out wire and switches.
HTH,
SB