Daylily is right, you definitely don't need as much stuff as Babies R Us would like you to think. I didn't co-sleep, so I did use a bassinet and later a crib. And I found a bouncy seat to be useful. I held my daughter a lot of the time, but when I couldn't, it was a nice comfy place she could sit and nap or watch me cook (I would put her up on the table and talk to her while doing stuff), and she also sat in it in the bathroom while I showered and sang to her to keep her happy!
I wouldn't necessarily get the cheapest carseat, although as daylily mentions, sometimes the extra cost is for unnecessary features. I would get the safest one. Check out all the safety ratings through Consumer Reports. Also, there's a good book called Baby Bargains that rates items like carseats, strollers, highchairs, etc.
You'll need some kind of baby bathtub, too. They make ones with a hammock-like contraption to hold the baby securely. They didn't have these when I had dd and I hated the way she slipped around in the tub. I wound up taking her into the big tub with
me a lot of the time.
I completely agree about those "smarter baby" toys. What really helps a baby's brain develop is interaction with other people, especially her parents. Talking and singing to your baby is free, and infinitely more rewarding (for both of you!) than those overpriced battery powered toys that say hello in seventeen languages!
Playpens have their place, too, depending on your situation. I never used mine to contain dd for my own convenience, but when she was walking and I needed to shower, it was a safe place for her to stay for fifteen minutes with some toys. We also used it as a portable crib when traveling, although if you plan to co-sleep you don't need that. Lots of playpens have been recalled so check them out carefully. Don't assume because it's still for sale in a store that it is safe.
So, beware of all the ads for gadgets and gimmicks that are supposed to keep your baby entertained or intellectually stimulated. Get what you need to keep her safe and comfortable, and remember that the most important accessory is you!