Considering an external HD, need some suggestions

I currently have enough storage in my new build, but the PC weighs in at above 50 lbs. Bringing it to someone else's house to share data would be a pain. I am looking for an external hard drive, as the topic says, but it can also just be an internal in an enclosure. I don't need more than 80GB of storage, I would think. (But no, I don't want a SSD.) I would like the total price to be under $100, and I would like for this to be pretty compact. An eSATA port would be nice, but from what I have heard, most external HDs with an eSATA port also require a power cable (which I don't want). I also need USB, because most of my friends have pretty old computers. I have heard though, that if you are using USB, you don't need the power cable to be attached. It is okay if the drive operates like that, because I will only be using eSATA at my house and I don't mind having it hooked up to power while at my house. This sounds pretty confusing, so if you need me to clarify on anything just ask.

Thanks always!

This seems to be along the lines of what you're looking for:

http://www.newegg.com/Product/Prod [...] 6822101059

It's $109 for 250 GB, but it was the only 2.5" drive with USB and eSATA which I could find. I don't know of any 3.5" external HDDs which can get their power from USB.

I don't really want to get a 3.5" drive, but I think that shouldn't be a deal breaker for me. If I find a great deal on a 3.5, I will get it.

Right now I like this combo: http://www.newegg.com/Product/Prod [...] 6817392016 and http://www.newegg.com/Product/Prod [...] 6822136099

On the "prebuilt" side, I am considering this: http://www.newegg.com/Product/Prod [...] 6822101058 <- This one seems to have a bad review though, but it is only one review so I don't know what to think.

So to slim down my first post, I am looking for total cost under $100, atleast a USB and a eSATA port (can be more), and when using USB, no other power cable should be required. When using eSATA I really don't care if it has to be plugged in somewhere else.