Wireless slates

I have been wanting to use a wireless slate.  I teach 4th grade and the Smartboard is so low that most of my kids cannot see over the heads of the kids sitting in front. They also do not pay attention until it is their turn. I use it a lot, but they still don't seem to be interested.

I would like some advice on a wireless slate. I have tried to learn about them on the internet, but it is confusing to me. I don't understand how JUST a wireless mouse is the same as a wireless slate. Can someone explain that to me? What do kids write on if there is no slate? I have read about wireless pens too. What do they actually write on? A special paper...the desk? Should I get a wireless keyboard and mouse?

I have a Microsoft desktop and an Apple laptop with wireless network. The smartboard is connected to the desktop AND the laptop so I can switch back and forth with the push of a button. I also have it hooked up to a receiver with speakers in the ceiling. All of this was bought just this year. I use the smartboard for interactive lessons AND as a glorified whiteboard to project tests since my clickers are a different brand. I project the student textbooks and all workbook pages. I think I have mentioned everything I have and how I use it.....so now I need to figure out how to get a cheap wireless slate or tablet. Is the tablet a PC or is it just a graphics drawing tablet? I can't afford a PC...I think I need a wireless slate because I don't want kids to move when I teach math. I want them to stay at their seats (for some things) and use the slate to show their work on the smartboard so everyone in the room can see. (remember that heads are in the way since the boards are so low.) Also, can only one be used at a time?  Do I only need one for that reason?

Any advice for what to purchase and where to purchase it? I have about $125.00 of school money to spend, but that won't buy everything. I will not be able to use the internet since I have to use a purchase order. I will have to pay the rest on my own. I know the wired version is cheaper, but it has to stay attached to the computer....no way to pass the slate around. I will appreciate any advice you can give me. Also, please give me lots of details.....technologically challenged here....for the most part.

Thanks! Peke