A few months ago I bought some paper off KiddyQualia from Etsy. Link to the store here.
For A5 fans there was heaps of choices.
As a lover of colour - these sets are amazing. I love the rainbow of papers used and I got both grid and lined papers. I also got another lined set for a friend.
I thought I would try out some pens on the Ivory pack that I bought. The paper is a lovely thickness, and the ink in all the pens worked well on its surface.
Here you can see that not many of the pens bleed through to the other side - the worse of course is the Sharpie - but honestly I've seen worse.
Now for price. I bought 4 packs which including postage cost me about $21 each. That may seem expensive, but then when you work out how much the original materials and how long it would take to print and cut your own paper to get the same product, then I think I would rather pay.