The cost of showing a heifer is a lot. Just like a steer a heifer will need to eat 2% of her body weight at all times. That should give you a good idea on how much feed will cost and a ruff idea of how much to get. As for supplies that is going to cost the same,
IF you live in Texas you are not going to want adhesives or glue because most of the shows are slick shear. IF you live north you are gonna want to figure in the cost of adhesives and glue (average cost is about $7.00/can.) Daily supplies varies depending on what you use. I use kleen sheen, vineager and shampoo (once a week.) Since you already showed a steer you wont have to buy a blower, showstick, halters, etc. I am assuming. If you have any questions you can pm me. Hopefully this helps you price wise.
Oh also if your calf needs supplements you will need to figure that, but you usually won't need to figure this out till later.