If I purchase from third party, am I then charged only 7.00 for the added service?
Not sure where else you would buy one as cheap, but Dish sold me mine for 25 bucks. If I remember correctly I think I read that you can only have two wireless Joeys connected to a Joey access point. Not sure whether two access points would play well together.
As well, when you own your Wireless Joey, you can activate and deactivate that Joey with a call to Dish and you're only charged for when the Joey is activated. So if you put it in the guest bedroom that's only used a few weeks a year you only need to pay the monthly fee for the active time you need. I do believe the fee is also prorated. So if the montly fee is $7, a weeks worth of use would cost about $1.75.