"Of course we want you to buy it. It's been years of our lives in the making, and we have bills too. However, if you absolutely cannot afford it, we'll make you a deal. Snail-mail us a postcard, and we'll email you a free copy.
A proper postcard, mind you, with a vacation-like scene, and an actual postcard stamp. Hand-drawn postcards are both acceptable and encouraged. The more effort you expend, the better we'll feel about our end of this bargain."