I have read a number of books on Sylvia Plath's life, one by Ted Hughes's sister, there is a collection of Sylvia's Journals which I also own which is fascinating, gives a real insight into her life and work.
The Bell Jar is a great read but I think that it is probably hard going if you haven't suffered from depression as it can seem terribly self indulgent and relentlessly morbid otherwise.
I can't believe it is so expensive to buy - have you tried Amazon or ebay for a R2?