The time involved in choosing a pattern, getting all of the fabrics (for a bargello it can be up to 24 different fabrics!) and all of the cutting before you ever get to sit down at the sewing machine can be hours. If you are able to sit down and spend hours every day, you can finish a quilt in a month....but if you are only able to sew for a few hours a week, then your quilt will take a few months.
The cost of a quilt has many variables, such as size, fabric quality, etc. I normally don't spend over $100 on fabric for the top, about half of that for the backing and then batting is around $30 (for a queen size quilt). All the little things required to make a quilt will add up too if you are a first time quilter....pins, rulers, cutting mat, rotary cutter, basting spray, pattern, plus a lot that I haven't added. Your time involved in the quilting process needs to be added into the price, making the final cost way more than you would ever think.
I would be interested in following your progress, posting pics and such. It brings me back to reality of the time I actually spend in the sewing room when I see what other people are doing. I could sew for hours and never realize that time has actually passed if it weren't for the hubby requiring a cooked meal!
I hope you have a great time with your quilt!