I would start accumulating everything you need to do a prenatal (stethoscope, BP cuff, doppler/gel, tape measure and wheel). Then I would ask your preceptor to put together either a list of what she wants in a precip pack or a precip pack for you.
You should be okay with those things for quite a while. Everything in your prenatal kit will allow you to do vitals if you're labor-sitting (okay, maybe add a thermometer to your bag), and will allow you to do a prenatal as well. The postpartum stuff (sling/scale, etc) are relatively affordable and you can add them as you go.
I find that people tend to really spend on midwifery equipment when you don't really need to. For example, I've been practicing for 4 years and don't have a Littman (though it IS next on my list!). My scale was $14 at Academy (I check it for accuracy occasionally) and I made my own sling for it. Buy what you can afford and when you have paying clients, you can replace it with the pricey stuff later--if you decide you really need it.
Charlotte, midwife to some awesome women, wife to Jason, and no longer a mama to all boys S ('01), A ('03) S ('08) and L ('10).