All temples have different prices,you can call around or go visit them.
There is no need(other then for your wife maybe)to have a Buddhist
kind of ceremony.
I have been to burnings where there were no monks at all,just shove them in
there and burn them.
You can have it done on the cheap but around 40k will send you off with
a few monks blessings.
Flowers alone will run 10000 baht already.
Make your wishes known and they will be respected.