A few options here, as always in the OSS world!
Simplest, if your pages are (say) 50 lines each, typing 50k will move you up a page. 150k up 3 pages, etc.
If the pages are separated by a new-page character (Ctrl-L from memory) you could search for that: / Ctrl-V Ctrl-L (use a ? instead of a / to search backwards)
Both of those could be mapped to function keys:
:map PgUp 50k
for instance. (Not sure about the "PgUp", you might need to refer to the manual for your particular version of vi...). Stick that command in a .vimrc file and it'll be permanent.
Hope this helps....