Spacers do work. 5-10 horse gained is reasonable but you have to remember that the gain is based on the engine its being put on. Like Matrixx already mentioned, long intake runners promote better fuel effeciency. Also, the spacer helps dissipate heat meaning that the fuel will be cooler which is why it can generate gains in HP. $40 doesn't seem bad but there maybe linkages and hoses that you may have to adapt since the TB will sit higher.
You could make your own, we used to do that in high school. We used wood. No, the engine doesn't get hot enough to ignite the wood and the best part was the carb was so cold.