For pre 1837 some libraries will send photocopies of marriage/birth entries. Charges depend on the library.
I think Birmingham charged £3, Surrey charged something like £4 for up to 3 entries, and some charge £0! And that £0 includes postage to Australia! Yes, you DO need to know the names, date and church, however with one of my Birmingham ones I just had name and date and the correct entry was found for me. (I've had great service from the libraries).
For post 1837 I use the GRO - £7 includes postage to Australia (!

) so not a bad deal. Costs more to buy Aus certs! If you know you have the correct b,d or m, you
never regret that £7 investment!