Honestly man, just get some seat covers until you can afford the seats. If you dye, be sure to buy dye with a flex agent in it. I've successfully dyed parts and had it looking pro, but stuff like seats, door panels, and high traffic areas are no places to have dye, as it usually wears quickly. IMO, an interior that "looks" dyed looks like ass, and looks mickey mouse as all hell. you don't want a mostly black seat with red chips showing through.
Save up a $100 and do the carpet the right way. Get some used takeoff mustang black carpet. I got some near mint oem 91 hatch carpet sent to my door for $100 shipped. It's much easier than the repro stuff because it installs in minutes with no cutting. Do this swap right, save until you are ready.