How much does this go for pre and post wipe?

Looting mk3. (Safekeeper)

pre and post wipe prices are almost the same since people save the bp's in another account

Not according to a few centuries of economics Thanks though

Its funny you are asking a question and cant accept the answer xD
Since this game has family share you can make accounts for free and store bp's there
most of the good traders have 20x each of the good bp's

to give advice on the price per fg
you can check the value of bp's for seeds (on another platform) and translate the seeds price to the bp price thats how people usually do it.
best of luck out there raider