The easiest low-tech solution is to use a pillow on your stomach and prop the iPad on that. There are even bookrest pillows out there that are shaped specifically for that and are in the $20-$40 range (check Amazon.)
I personally don't like the pillow solution. I don't find it comfortable and a bit too hot in the summer.
There are also some floor-standing holders that can be used to hold it in bed or while sitting that I prefer but up to now they have been too rich for my blood (e.g. $175 for this one: http://www.bookholder.com/item.asp?n=33478
I recently saw the one I'm planning to get announced called the iProp for ~ $80: http://www.iprop.com/index.html
. It's still $80 but I'm willing to pay that for the convenience.
And no, I'm not associated with the vendor
I just also find it too heavy to hold for long periods in bed.
Good luck in your hunt.