I don't have an explanation, but I can tell you this is "normal" of GE/Frigidaire. You never know what to expect in terms of pricing.
The original part # was 5304452068, has been substituted to 5304470638. Maybe one will pop up on ebay eventually but I wouldn't hold my breath.
If it were my dishwasher, i'd buy a $500 Bosch (much better dishwasher than ANYTHING Frigidaire sells) and call it a day.