Export the whole table to Excel.  Reinit the IM_PriceCode table.  Edit your spreadsheet to remove everything but what you want to keep.  Import using VI.  Do not try this without testing first.

(You can even do all this in a copy / test company, and copy the IM_PriceCode file between company codes).

I've also done this by script, when a customer wanted to delete individual PL's on demand.