My my, they really try to soak you. $15 a day for a GPS unit. So I figured it out, for 8 days I was looking at $120 to rent a GPS unit.
So the web to the rescue. I found out Radio Shack was selling the Tom Tom 125 for $97 which with RI sales tax of 7% or $6.79 (Disgusting I know, when MA is 5%) it came out to $103.79, a $16.21 difference and I own it.