First time painter shoping list?

yes it is not cheap but think of what you're saving by DIY as opposed to paying someone to do it for you. Much of the material you can use for future projects, paper, guns... and so on. So it is not just do the floor and done.
If you plan on doing the whole car in the future? You may want to buy rolls of 80 and 220 etc as it is a lot cheaper for a roll of 100 sheet (25.00) than 4 or 5 disks of it at 5.00.