The gas tank has to be dropped in order to get to the sending unit. That’s why I’d live with it.
Tester
@commonsenseanswer I know this may be “somewhat” off-topic, but when I worked at the Benz dealer, there were quite a few models in which the fuel pump modules were accessed from the BOTTOM
My Cadillac has an access hatch in the trunk for the fuel pump as well. I’m not a professional mechanic, so it would take me more than an hour, but if the OP’s car also has an access hatch, $555.00 is nuts!
EDIT: Didn’t see @Tester’s comment above. 
@db4690, I’ve Not Seen That On Any Of My GM Machines, But I Had A Chrysler Or 2 That Had The Module Accessible High And On The Back Of The Tank. My Chrysler (Dodge) Caravan Allows Access By Just Loosening The Tank Straps, Without Dropping The Tank All The Way Out. I Watched While They Did A Module Seal Recall Many Years Ago.
CSA
The price does not mean there’s any ripoff going on here. The sending unit is more than likely only available one way; as part of a module which includes the fuel pump itself, mounting bracket, and so on.
Complaints about methodogy should be directed to the company that built the car in the first place…