Wow!
So many awesome responses!
First let me say that I am indeed getting some more bids. I have 2 more companies coming out next week to take a look (1 a concrete company and another a landscape company). I've been having a hard time finding people that do this type of work in the yellow pages. My wife works from home so getting people out for an estimate is not a problem.
smschulz, I agree! No way I'm mixing this 1 bag at a time.
cx / hammy, so do you do a monolithic slab / footing and put the poly under it all?
scuttlebuttrp, we definitely do not have the room for a truck to backup on our side yard

That would be much easier. Though I did do the calculation and using a Georgia Buggy would only take about 3 trips to get all the concrete transferred from front to back. Not tooooo bad.
jdjanka, that does sound like an incredible price! A little over $4/sq ft sounds like a heck of a deal. I figure it'll cost me somewhere between $5-700 to do it myself with the cost of concrete, form boards, rebar, and tool rental. If I could get someone in the $1k range I'd jump all over it.
Davy, I'd love to do stamped and stained concrete, but there's just not enough room on the existing patio to do it and I don't want to have mis-matched sections. Also, recovering the existing patio would certainly put me way overbudget.
Another comment / question. My existing patio was poured directly on the dirt in the back yard, no excavation was done. Then the sod was laid so I currently have a drop off from the existing patio to the grass as shown in the first pic. The second pic shows that there is not much patio under the existing grass. I don't anticipate needing to dig out much of the dirt and I'm wondering just how flat the pour area needs to be? Do I need to really work it or just get it close (assuming I do not use any crushed stone and do use a poly barrier).
Thanks again for all of the great info so far! I'm learning a lot as I go along

Even if I do end up going with a contractor, I now have the knowledge that I need to evaluate the folks giving me estimates.
Russell
Russell