You can check out the best online MBA at Washington state . It is about 40,000-50,000 USD.
The tuition , in terms of the credit hours at a average B School , is about 1000-1200 per credit hour , and it typically takes 60 credits to graduate . You can calculate yourself.
just from what u said "读完MBA后是否继续读博做研究还不确定", I suggest you reconsider this. There is absolutely zero relationship between MBA and PhD/further research. If you don't even know this, you have a lot of things to learn.