MacBook White Battery-buying issue

[Matt23]

Hey all, as you can probably gather, my MacBooks battery has died. I went to the store yesterday and they're after £101 off me for a new one, to which naturally I thought you can **** right off. Been on eBay and a number of sellers seem to be doing them for between £20-30, wondering if people could let me know from experience if these items are the real deal or if they are too good to be true? Really don't Wana part ways with £101 for the sake of a battery, cheers