About 5 years ago I thought I HAD to have a serger. I bought a very nice used one off Craigslist. It looked like it just came out of the box. In fact, it was packed in the original box. It is a Singer and I think it was $300- 400 new. I also got about 30 cones of thread with it and payed $80. Yes, the threading was a bear but I just took it one thread at a time, following the manual step by step. I will tie new cones to the old ones so I don't have to re thread it when the time comes. That being said, I have yet to use a full cone of thread. I broke a needle a couple of years ago making pajama bottoms for Christmas. The serger is in the cabinet STILL with the broken needle! I am glad I didn't invest a lot of money into it because I really don't use it very much. The reason the guy was selling it???? He didn't use it as much as HE thought he would!!!
As for your pillowcases, I do a French seam on mine and they results look very professional!!!
http://m.youtube.com/watch?v=U0HGkuuGw6w