So....you think you will get one covered for less than $600....that's lineball IMO. Do your homework, but it is hard to find a business that does Skyline type wheels. We fall into a black hole that nobody cares about/ There are restorers that work on older sold wheels for Chevies and EH Holdens etc, then there are those that work on R35/Porsche/BMW wheels. I found it very hard to find anyone that works on our era cars...nobody seems interested.
Try a few upholstery businesses, but I'd doubt you will get it that much cheaper, as GTSBoy said, labour isn't cheap. And a Momo in good condition will set you back over $1,000. Remember you will need to keep your airbag setup.....and that raises the cost.