I would not normally recommend getting rid of a good metal singer that you like, but you might get a good deal on a trade-in. If they give you $50 or $100 for it, it could bump your budget up to a better machine...
On the whole, I really discourage folks from buying machines under $200 as most of them are really cheaply made and give you grief when you try to sew through thick layers (think about hemming jeans), sheer or slippery fabrics, knits, and other interesting and fun fabrics (like costumes).
I have seen some good introductory/student machines made by Brother and also some Kenmores. The deal with Kenmore is that just about anyone can make a machine and sell it at Sears under the Kenmore name. So you might be getting a Janome or Brother and you might be getting a really low-end Singer. There is no telling. The other disadvantage to buying at a big box store (Target, Costco, etc) is that there is no one there to help you with the machine.
I really recommend finding a sewing machine dealer and shopping to see what the introductory machines are - what features are available (and which of those you will actually use).
I would recommend looking at both Brother and Janome, but I don't know what their least expensive machines are. They may start at over $300. But Janome makes a lot of really excellent machines and if you can afford it, I would go for that.
(All that being said, I sew on a Bernina. But they start at $500+ I'm pretty sure.)
Good luck and have fun shopping!
Sally the Sewing Teacher (
www.sewsally.com)