The Brother PE150 is the bottom of the line starter embroidery machine. For one in good working condition you shouldn't pay more than $150-$200. They are dependable machines and have a good resale value. The PE150 is sold under a variety of names, such as White.
You can get a Bernina 600 for around $300, a Bernina 650 for around $350 in good working condition. The 600 is a step up from the 150, the 650 is a step up from the 600.
These machines may cost more if they are including the PED Basic software, which allows you to download designs from your computer, or design cards.