Regarding price difference, it depends what you consider significant.
On Apple's site, the base Macbook is listed at $999 with 2 GB RAM; that might be enough for Mac OS.
On Dell and you can find a laptop with similar or better specs for ~$800. Example 4 GB RAM (recommended for Win 7), bigger hard drive. And that is list price. There are lots of sales and you could get it for ~$600 without much searching. If you are patient, you can get a lenovo laptop of similar spec for $400 on sale now. Competition is good for the consumer.
I would really recommend avoiding a single core computer especially if you intend to keep it for a long time. Older dual cores are not that much more than single core, and even if you don't multitask the second core can run service apps behind the scene and your computer will be noticeably more responsive. In the future more programs will be multi-threaded and the advantages of more cores will become greater. Any single core machine will be a very low end machine that you will probably be disappointed in. That is one reason you hear more people complain about Windows computer than Mac. Some people expect a $400 Windows laptop (not on sale) to be as fast as a $1000 Macbook.
Regarding Asus, they are the premium motherboard manufacturer and their other products are generally quite good.