If you gave a good midwife system in the hospital you are going to give birth then as Lulu said you probably wouldn't need an OB.
I think under the MW system you still see an OB once during the later stages of pregnancy.
I had an OB for all my pregnancy's. I went private so I think I had to have one? I went private as I wanted to stay in hospital as long as I could. So this was 5nights.
I probably could have done without as mine were all non complicated pregnancy's and births. It was what I felt comfortable with.
What I did like about an OB as I was pretty much in control of how I wanted things to go (baby co-opereating of course). Most MW are like this too, although I had a friend who went public without an OB and the MW were not great at listening to her and her needs.

Some hospitals now have the KYM (know your midwife)scheme which is fantastic, you get to see the same MW through the whole pregnancy and she/he will be there at the birth too. Worth investigating.

Also..the amount you are being charged by your OB is very reasonable. Before this new change 1st Jan most OB'S were charging double that so perhaps the new system has done what it intended it do and bring the price down OB's charge and make them more available and give people a choice of MW care of OB care.

I look forward to hearing everyone else's experience's.