Kirk Hinrich has a deal for about $9.5 mil per (5 years, $47.5) , and you know his agent would argue he's better then him.
The argument from his camp probably goes he deserves a contract in the Deron Williams (4 years, 70 million) and Chris Paul (4 years, $68 million) range, especially based on the playoffs and basically averaging a triple double. The C's would argue he's not on that level.
Mo Williams and Jameer Nelson both seemed to break out after getting their contracts, so you probably can't compare Rondo's worth to theirs:
Mo Williams got 6 years, 51.5 million
Jameer Nelson got 5 years, about 33.6 miliion
Rondo is probably going to get something around $12 mil I'd say.
So quick rundown of other young point guards and their extensions after rookie contracts:
Deron Williams, 4yrs/$70M = $17.5 per year
Chris Paul, 4yrs/$68M = $17 per year
Kirk Hinrich, 5yrs/$47.5M = $9.5 per year
Mo Williams, 6yrs/$51.5M = $8.6M per year
Jameer Nelson, 5yrs/$33.6M = $6.7M per year
(my numbers may be a little off or inaccurate, just pulled from various websites)