If Vlade and Co are comfortable enough making Rondo our top target and want him as our PG, 10M/Y isn't too much. It's our cap space this year but next year with the huge cap boost, 10M/Y is peanuts. Offer it, say 3/30 and protect ourselves with a team option.
You can't make Rondo the priority, then haggle over a couple mil. I seriously question the fit but if Vlade/Karl are both on board with them, they must have a plan on how to use him. Freeing up cap room to get shooters to put next to him would require creating more cap space through trades/stretching Landry, things of that nature, or acquiring those players through trades. If the idea is for 10M we're going to get Rondo and a shooter to put next to him, that ain't happening.