As long as you are billing the charges out consistently. In other words, you can't charge one insurance 3 times the price of the implants because they pay a percentage of what you bill, but only bill another the cost of the implants. I would come up with a formula that covers the top paying contract you have and stick with that across the board. For instance, marking up all the vendor invoice amounts for HCPCS C1713 by 150%. For those insurances that pay based on invoice cost, you would need to submit a copy of the vendor invoice with the claim. The insurances would then be responsible for any contractual adjustments. However, be careful to watch for overpayment procedures/guidelines outlined in the contracts. Most state you would be responsible for returning any overpayments.
Since the price of the implants usually depends on the quantity, type of implant, etc., marking up by a percentage would be the best option. However, if you only bill a few specific items out under a specific HCPCS code, then you can always just charge a flat-rate. The key will be consistency! The guidelines your practice or you implement when deciding what to charge has to be the same across the board for all payors, including self-pay.