Your OB can refuse you care for whatever reason he feels like when it comes to you refusing tests. It just depends how s/he feels about it. There may be some things that they are willing to let you skip because of personal preference, but other things are mandatory. You just need to talk to him/her. They won't just kick you out, but they will refer you to another OB. This was the case for my friend.

Also, I'm military as well, and as long as all the tests were ordered by the doctor, I never had to pay for anything. I had a complication with my last pregnancy and they payed for all the extra care I needed. With my second pregnancy, I went in for emergency stress tests several times and they were covered as well.

If its for the baby..... I wouldn't refuse something that was the best for my baby. That's just me though.

I would also suggest asking Tri-Care about a possible mid-wife rather than an OB. They may cover that.