A lot of us were wondering the same thing, so we started posting what we pay and generally where we live (to give you an idea how different regions of the country can affect prices).
I'm still waiting to get my new puppy. I have asked around DFW and found $55-$65 the norm for a toy poodle. Some places price per service, so it can be a lot more/less depending on what you need or what style you want.
I had my previous poodle groomed every three weeks and she stayed pretty fluffy. You can stretch it to four weeks, but it would be hard to go much further without some touch up work.
It's also important to comb/brush them daily if you can. Longer hair tends to get matted, especially in the arm pits.
One more thing... If you do try to stretch time between groomings, really be careful about the hair matting. Sores can develop underneath and attract bugs, not to mention getting infected. I have never had this happen and would find it negligent for anyone to let their animal get this bad. People who haven't had a long-haired pet may not realize how bad it can get in a short amount of time.
You can ask some of the groomers here. They hate attempting to de-matt or will refuse to do it. It's time consuming, and it hurts the dog. Leaving little option but to shave the hair off. Can you imagine being shaved with sores on your skin?
Groomers will charge a LOT more if your dog is matted, so you won't save any money if you try to go too long and don't maintain their coat. I know one grooming salon charges $5 every 10 minutes. It can take hours. Better to be on a regular schedule.
I would always make my next appointment before leaving the salon.