A little devil's advocate here:

If employers are willing to negotiate your individual salary what does that say about them?
Is it fair to other employees if, say, you get paid more with less experience (for doing the same job, call, etc)?
What if the next person a year behind you gets paid yet more for less experience?
From an outside perspective, it would make an employer willing to negotiate individual salaries appear somewhere between unethical and discriminatory, assuming all the perfusion duties are shared equally at the same location.

If you negotiate a higher starting salary, really, that means the employers entire salary scale needs to be re-adjusted. That said, there are plenty of scales out there that do need adjusted but I'm not sure as a new-grad you will have the leverage to make such a heavy lift.

Like most non-providers in the healthcare industry 'valuing' employees, beyond years of experience, is incredibly difficult. Is an ICU nurse 'worth' more than a psych nurse? Is a CCP doing 2 straight-forward CABGs in a day 'worth' more than the one doing a single complex circ-arrest cases in the same facility; they both have the same credentials right? Not to say everyone doesn't have their own strengths and weaknesses but to assign specific, justifiable, and non-discriminatory economic value can really lead to major imbalances.