I am with Cliff. I would hold out til you had time to fill the walls with your own designs. I had to discipline myself to work in one a week to get it going. Here are a couple of ideas:
I saw a really creative display in a shop somewhere using empty frames, in some cases nested. This might be a short term fix. If you are a perfect measurer, maybe you won't have any, but I always seem to have some hanging around waiting for that job that will justify cutting them down.
I have had good success buying sheet mirror stock to put in "mistakes." It is amazing how many times I hear "I didn't know you could make mirrors!" I usually sell them right off the wall with prices that are competitive with the big box home stores like Lowe's & Home depot. But my mirror frames aren't plastic. This is quite quick and easy.