AnkerDirect via eBay is currently selling refurbished Robovac 10s.
They are priced at $99, so this is a very (relatively) inexpensive option to get a robotic vacuum.
eBay says 37 have sold and over 64% are gone. If you do the math, that means no more than 20 were available at the time of this post. I suggest you jump on this deal ASAP!
BONUS: If you purchase anything else from Anker on eBay, you will be rewarded with 10% off your entire order!