Do you have an area that you can use to feed just the calves? If so rather than buying a creep feeder you could use a board over and open area or set a metal post so a gate would only open far enough to let calves in and then feed them in a bunk or pans. Kind of hard to explain but any opening that would allow the calves free access but not the cows should work.
Check with Tractor Supply...they carry a Behlen model that is galvanized and poly. 2 different sizes and they are affordable for a small amount of calves. I've got one and it's held up well.