Here's my situation and I need advice please!

So, my SIL texted me the other day and said to pick out a present for the baby now so she can start working towards it. I have no idea what that means, is she talking about an expensive present? But what's the price range? Should I even ask? Or should I just start registering and tell her to look at that instead?
Oh and my MIL wants to do a girls shopping trip of just us two. We're not close so this would be my first time out with her, alone. I'm nervous because what do I pay for and what should I even be looking for?
Since these two are family, I feel more awkward telling them what I want because I don't want to go over boundaries. If these were friends and what not, I would just tell them about the registry (when we do start one).
Ugh, I get so awkward when people wanna buy us stuff (except from my parents because I'm used to them buying me stuff all my life).
Re: Receiving presents etiquette
MIL situation, you are brave to consider that since you have never been out alone before and this is a high emotion situation involving her wanting to spend money and the parameters aren't well defined and you aren't sure about this. If it were me I think I would tell my husband he would suddenly, "want to be included" to spend time with the wonderful ladies in his life and would tell his mom this and tag along.
Either that or set a time limit for this time with MIL, or another plan is in advance between you and your husband and/or best friend - pre-plan some "out" plan if needed, and also know the agenda of what you need/want before you just "go out shopping" since you are already unsure of the situation. I think it is wonderful she wants to do that with you though. She must be pretty excited.
Ask your SIL what type of gift she was thinking she wanted to get your LO, this will give you an idea of the price range. Or simply tell her to choose something off the registry.
I would DREAD going shopping with my MIL, you are brave. My MIL annoys the crap out of me with her opinions of things I should and shouldn't do. In this situation I would probably make DH ask the questions of what she's planning on buying/spending. It's his mother and he should be able to find out her intentions without any problems.
Good Luck!!
Anyway, I third recommending they check out the registry. If they don't like anything on it, they can buy or make whatever they want.
For the shopping trip, anticipate the possibility that your MIL will see something she loves, like a style of furniture or crib, that'll clash with your plans. Maybe have a polite response prepped if you have to nicely turn down any of her ideas.