Andy,
When I did my mep/meir renewal earlier this year it was very similar to the original test. We covered just about everything as per the initial. The only difference was perhaps the examiner who was a little bit more lenient. I cocked up the efato on the go around and forgot to feather the prop. Nice chap that he is, he repositioned me back on the ILS at 4 miles and made me do it again. Needless to say, i didnt screw it up that time!
As for cost, the examiners fee was £200 for test. Aircraft hire was obviously on top of that.
Hope thats of some help.
As for the SEP/MEP question - two totally seperate ratings(as per your licence), so unfortunately you'll have to renew your SEP.