Zocor usually works as well as Lipitor in most people, with no difference (or perhaps even fewer) side effects, so long as they are taking equivalent doses: 10 mg. of Lipitor is about the same as 20 mg of Zocor, if I'm remembering the ratio correctly. So if he was taking 20 mg of Lipitor, his simvastatin dose should be 40 mg.
There should be absolutely no difference in generic simvastatin than the brand name Zocor, unless there is some manufacturing error (which could happen with the brand names too).
Crestor has a higher incidence of side effects than either Zocor or Lipitor.
I'd try the generic simvastatin for awhile, but if the cholesterol numbers after about 3 mos. are not pretty close to what they were with Lipitor, I'd consider paying the higher price for the Lipitor. Are you sure the insurance company won't pay for it at all, or that it's just that you have a higher co-pay, e.g. with my company, I pay $10 for generics, $20 for "preferred brands" and $40 for everything else. Also, most insurance companies have a "prior authorization" and/or appeal process, so if you have proof that the Zocor doesn't work as well, with your doctor's help, you may be able to get approval for the Lipitor (but you'll have to fight for it and not give in/give up to the bureaucratic barriers they will put in your way, like telling you the first time you call "we don't cover it." or requiring tons and tons of paperwork.)