It really depends on what your style is. I was a t-shirt/jeans girl and while I could have gotten away with bigger shirts it would have made me look frumpy. I got some shirts on sale and I look sooooooo much better in maternity clothes than just bigger clothes. I already have body issues so that was nice for me.
You can try looking for sales, looking at auction sites, or even at thrift stores. You also can get a maternity STYLE shirt that can be worn after you have the baby.
Any shirt that is peasant style or empire style can look good both before and after the baby. Here is an example of a shirt that would work https://www.amazon.com/MOD-Womens-Smocked-V-Neck-Green/dp/B00ED476P6/ref=sr_1_33?s=apparel&ie=UTF8&qid=1390268620&sr=1-33&keywords=empire+styleThere are a lot of dresses that work and look good with maternity and also can be worn afterwards. Keep in mind that you won't be walking out of the hospital in your normal clothes with a baby, lol. It takes awhile for everything to go back down. I would say I looked about 4-5 months pregnant the day I left the hospital.
i would say that about half of my "maternity" clothes are normal clothes that I bought at normal stores for normal price that I knew would work with a bigger belly.
As far as nursing, during the beginning I spent most of the time (at home) wearing a nursing cami (around 12$ from Walmart) https://www.walmart.com/ip/Bestform-Maternity-Nursing-Tank/10843537 and pj's. If you go out you can pair them with a sweater and pants and they would also work.
I bought a few shirts that had ties or elastic drawstring around the neck (not specifically sold as "nursing") at Walmart really cheap, kind of like this https://www.amazon.com/Bandolio-Womens-Sleeve-Peasant-Olive/dp/B009XS2MY2/ref=sr_1_28?s=apparel&ie=UTF8&qid=1390269872&sr=1-28&keywords=peasant+shirt Anything that buttons up is also good. I had a nursing cover, but I didn't nurse too much on public (I think more people should, I just have body issues so never felt comfortable).
After I got the hang of it it was no problem to wear my own normal clothes and just pull it up or down depending.