The fuel pump is expensive. Do you have to replace the entire fuel pump to fix a sender that is not working? What other causes will make the fuel gauge not work?
Only problem is that this 2003 XP DI actually does have a combination fuel pump/sender assembly. So it wouldn't surprise me that is how much it actually costs. It is not the same as the baffle-only setup in the older Seadoos.
That said, you have nothing to lose on removing the original fuel pump assembly and seeing what is going on. You already know it needs to be replaced - so take it out and take it apart. Maybe a broken wire, junk inside or something else that you can DIY fix. Worst case, you have to buy a sender - but wasn't that where we started anyway?