Factorio is currently ranked #3 overall (#2 for games with more than 1000 reviews) on Steam (98% recommended with 26.3k reviews). The price is currently $20. The developers have mentioned that Factorio will never go on sale however they are
planning a price increase to $30 on April 16, 2018 to coincide with leaving early access. If you plan on purchasing Factorio and want the lowest price possible you should make your purchase before then (you can get a slight discount (10%) on HumbleBundle if you're a HumbleMonthly subscriber).
They have a demo available on their Steam page. The 4 demo missions run you though the basics of setting up a base/production line and basic defense. I highly recommend running the demo if you're at all interested in Factorio (or run it through zlo). I just tried the demo myself and promptly purchased the full version.
