Wedding Cake on a Budget

Hi all,I could have sworn I posted about this last night already but I can't find the post. Alas,here we go again:
For budget reasons we are considering to get a cake from Waitrose or M&S or maybe get one courier delivered by Cloud Nine Cake Center. However, I'm unsure if this a crazy idea, because we will be spending the two days leading up to the wedding in a hotel. So I would have to either decorate the cake in our hotel room and then transport it to the venue *or* I ask the venue if i can decorate it in their kitchen.
- Am I delusional for considering this ? Does it sound like a bad idea ?- Has anyone had any experience with Waitrose or M&S cakes or with Cloud Nine Cake Center ?
Thanks so much.