Products page gives me the white screen of death - php memory exhausted


Everything with my Marketpress install seems to work fine, apart from my /store/products page. I'm getting the white screen of death on that URL, (but not the /store URL) and I've worked out that it's a "fatal error: php memory allocation exhausted" error. My allocation is set at 64M, and my host won't put it higher.
I'm running WP 3.1.2, Buddypress, and just upgraded to the latest version of Marketpress. No change. I'm also caching everything with W3 Cache.

Any ideas? I've got about 40 products, with about 25 "live" (ebooks).