This may not help, but I bought magnetic paint for my daughter's room. And it too had very mixed reviews. After painting the recommended number of coats it did not work. We had to paint 3 extra coats before it worked well enough. I'm not sure if the paint is at all similar, but that may be something to keep in mind if you do it and it doesn't work.
We have a white board on my DD's easel that we use. I bought that off
Amazon for I think $24.00 including shipping, and I used about $10 in Swagbucks gc's to get it for even less. It's somewhat small (I think it's the Step 2 Easel), but it's good enough for what we need right now. It's a chalkboard on one side and magnetic white board on the other. The kids use it all the time, and I use it a lot when working with her on math, ect. Another product that I LOVE is dry erase sheets. It's a clear pocket that you can slide any paper into to make it dry erase. They're $1.97 each from Lakeshore Learning (at least they were when I ordered a few months ago) and they work great. My kids love them too. I like it cause I can print out math worksheets and my daughter can get more than one use out of them. I've also bought small workbooks from Lakeshore and I put those in the pockets too, so we can use them more than once. The workbooks can get pricey and I like that my DD can do them multiple times if necessary and I can save them for my younger DD.
Lakeshore also has lap sized white boards that work well for I think $2.97. We have the blank one as well as the lined one for learning to write. My kids like these alot. Sometimes I will write the math problems on the white board and they use their lap board to figure them out. You can't beat the price and it saves on paper.
And for Dry Erase markers, I've recently found them at Dollar Tree. We go through a lot so this was a good deal for us.