When it comes to incubators, the phrase "you get what you pay for" is a very apt descriptor. What you save in money you'll pay for in failed hatches and dead embryos. I have a friend who uses one of those styrobators they sell at farm stores for $60 or $70 and out of maybe 100 eggs I've seen her set, she's produced about 10 chicks.
The cheapest decent incubator would be the Brinsea Mini Eco. It runs about $100 and will last for a good long time. It's far from automatic - you will need to turn the eggs and add water by hand - but it will hold temperature and humidity with reliability. Mini Advances are even better, as they have digital controls and autoturning features, but they leave the range of inexpensive at about $180 each.
Brinsea is a good brand. Excellent reputation. But the Mini Eco only holds ten eggs. If you're going to be incubating more than ten you'll need either the Incuview or one of the Brinsea Octagon models, which are all much more expensive than the Incuview.