I'm in my third trimester of pregnancy and I've spent less than $100 on maternity clothes. I've had a hard time finding national averages for how much women spend on maternity clothes, but I've seen estimates ranging from $400 on a bargain website to $1200 on MSN money. One of my favorite frugal bloggers, Penny Saver, who is a never-ending source of inspiration for me, spent almost twice as much as I did on her maternity wardrobe, so I think I'm doing pretty well.
The first thing I did was evaluate my existing wardrobe to see what would still fit my growing belly. I was surprised how much still works for me. I had two empire waisted tops, two turtlenecks, a long sleeved tee, two polo shirts, two sweaters, and five dresses that fit me. Serendipitously, I prefer shift and wrap dresses; both styles work well as maternity dresses. I also had one sweater dress and the knit simply stretches over my bump. Cardigans, scarves, jewelry and other accessories should not be overlooked either as all of these pieces will fit you throughout pregnancy. (Simply don't button the cardigan.)
I think one of the reasons I was successful at finding so many pieces in my own closet that work for me is that I was very careful in how I thought about things. I spent a lot of time going through everything and trying things on. Have you heard that saying that you wear 20% of your clothes 80% of the time? Your potential maternity clothes are probably in the 80% of clothes you don't wear very often/have forgotten about. Seriously, take an afternoon and try a bunch of stuff on.
Though I already had a lot of stuff I could wear during my pregnancy, I had to buy a few things to fill in the gaps. I bought:
1) a maternity band, which helped me wear my regular jeans into the second trimester. This is the one I have. I don't know if it is better or worse than other types, I bought it because it was cheaper than others I saw.
2) maternity jeans. All of my pre-pregnancy pants are mid-rise, which are not very forgiving with a swelling abdomen. If you typically wear low rise pants, you may be able to get away with not buying maternity pants. I bought these maternity jeans when they were on sale. I had to get them hemmed (at my dry cleaner's) which added to the cost, but even with the cost of hemming they were WAY cheaper than any jeans I saw at specialty maternity stores.
3) two pairs of leggings. (In retrospect, I wish I had only bought one pair. I haven't needed two.) I knew I had a lot of dresses already in my wardrobe, so my plan was to pair them with leggings to get me through the winter. I bought these online from JC Penney when I bought the jeans.
4) a pair of pajama pants. (In retrospect, I wish I had bought two pair because I live in these.) I bought these from Old Navy. They are regular (non-maternity) PJ pants. I bought them two sizes bigger than my normal size and they are glorious. Hands down, my favorite outfit is one of my husband's undershirts and these oversized PJ pants. It is a personal tragedy for me that I can't wear it out of the house. I wear it to bed and for lounging, too.
5) extra undies. Some women, including me, develop a problem during pregnancy where it feels like your crotch is bruised. It's simply a result of increased blood flow to the region, the baby putting pressure down there, and your body loosening up. I heard going commando or wearing bigger panties can help. I bought new panties two sizes larger than what I usually wear. They are the granniest of granny panties, and you know what, I don't care one bit. They're comfy.
6) a caftan. I was given a caftan from this etsy store for Christmas. (I'm not counting its cost in my total since it was a gift.) It is incredibly comfy and though I just use it for lounging, theoretically I could wear it out too. I'm thinking about wearing it as my post-delivery coming home outfit since I think it will be easy to nurse in. I am also thinking about buying another one for post-pregnancy.
The reason I listed my sources for things (none of the links are affiliate links) is because I want you to notice that I didn't buy anything from a maternity store. Maternity stores are a rip off. You're going to pay a ton of money for poor quality clothes. I'd rather spend that money on cute baby clothes or on decorating the baby's room.
In summary, to save money on maternity clothes I would suggest you try to reuse as much of what you already have as you can. You should consider buying regular, non-maternity clothes two sizes bigger than what you normally wear because simply being labeled "maternity" carries with it a premium price. If you do need specific maternity clothes, shop sales and clearance at department stores rather than specialty maternity stores.
Maternity clothes are not investment pieces for the rest of your life; you're only going to wear them for a few months, so you might as well save some money on them. Although my maternity wardrobe is small (it all fits in one dresser drawer) I have more than enough to last me the whole pregnancy, spanning three seasons, and I don't feel like I'm wearing the same thing everyday. And even though I am a housewife, I daresay that my maternity wardrobe would work just as well if I worked in an office.