OMG! That is insane! I definitely think that the WP should be involved in the shower, but my feelings are that if the WP is hosting, it shouldn't be expected to be a huge elaborate and expensive shower! For example, we just had a wedding shower for my good friend this past weekend. Her FMIL insisted that her gift to my friend was this shower which was a full blown sit down 5 course meal, centre pieces, etc. Just the lunch for everyone was $2000 plus the gifts for the guests, decorations, and all of that other fun stuff. There is no way that I would have endured that cost if I was responsible for hosting. I know that sounds bad, but a typical shower for me is at someones house, in the backyard for a minimal cost.
How did you get stuck with the bill? I would definitely sit down and explain that you are maxed out and need help!