Freecycle, yard sales children's resale/consignment shops. Check for product recalls on safety items like car seats and strollers - usually the resale shops are careful about this but yard sales and CraigsList, not so much. Babies outgrow clothing so fast, most of what you find in resale shops is in really great shape.
Also help your daughter to prioritize what she NEEDS vs. what she WANTS. She absolutely needs a car seat to take the baby home from the hospital, but she doesn't need a lot of clothing or toys especially in the beginning. A newborn doesn't need a crib or shoes, for example. Help her to separate what is a necessity from what is a luxury.
Make sure she is not focusing on all the cute stuff and is more focused on her health and getting prepared for parenthood. Unless she's due to deliver in the next 6 weeks, she needs to completely focus on learning parenting skills, infant development, prenatal health care and so on. Too often, teens focus on the "stuff" and not on the "substance." Their brains are not fully developed, particularly in the part of the brain that deals with consequences and planning, so she needs the most help there. You're going to have to take the lead there because she just isn't capable - her brain won't be finished developing until age 24 or 25, so you will need patience and persistence.
There are great books in the public library and every library has a lending arrangement with other libraries in the same system (so she should not spend money on books she doesn't need to keep). Enroll her in a prenatal class, a parenting class (basic first aid, how to change a baby, and so on) - and some of them have great accessories like those dolls that cry and need changing and so on, so the teens can practice dealing with a baby who cries and you don't always know what the problem is. It's a pain but they might as well get used to it! It really saves aggravation down the line!
Sometimes your town's department of Family Services has classes, but they can also make great referrals. Use all the free services available to you and to her to get her the counseling and preparation that will help her be a good parent. They can also help with a budget which helps teens (and others) see what's feasible in terms of holding a job vs. daycare, how to allocate money for formula (which may encourage her to breastfeed), what it costs for apartment/electric/heat, and so on. She'll realize she can't have expensive cable TV and lots of cute toys - the sooner that happens in her pregnancy, the better.
Good luck!
