That's a tricky situation for sure. First its your first job and second you are not good at pricing yet and your unsure about the whole job. I'm am not knocking you one bit I have been there done that like many of us and sometimes you just go for it or you walk away. 15 yards of mulch is close to $2,000 to install and beds and such plus trimming and more. Close to a $3,000 plus mind you I'm in Canada so the price is a bit off.