yes, doctors from different medical group can

bill different amount for same procedure, sometimes, the difference is huge.

For out of network bill, insurance companies have no authority to adjust the allowed amount, but pay the pre-stated %of whatever the out of network doctor/hospital billed.

For in network doctors, most contract is fixed fee schedule, no matter how much those doctors charge, insurance companies just pay according to fee schedule, mostly the fee is based on cpt4 codes. In that case, it doesn't matter how much the bill is, only if the billed is below fee schedule, the doctor get 100% billed, but it almost never happens.