Sprint had been touting its unlimited plan for $50 per month for quite a while, but now the carrier has quietly increased its unlimited data plan by $10 to $60 per month. The second line is still $40 with lines 3 through 5 being free through January 31st, 2019. So that's effectively 5 lines for $100 per month, which is still a steal for 5 lines if you're on Sprint, but remember that after January 31st, 2019 the price will increase for those additional lines. Line one will still be $60, line two still $40, but lines 3 through 5 will be $30, bringing the price up to $190, almost doubling it.
With Sprint's unlimited data plan you'll get unlimited data of course, with unlimited talk and text. But as far as streaming video goes, you'll be stuck with up to 1080p. Which is fine, since most people can only stream at 1080p anyways for various reasons, and there's very little content in 4K right now. Additionally, gaming is limited to 8Mbps and music streaming is 1.5Mbps, which is still plenty, especially for music, seeing as even HiFi audio streams at a lower bit-rate than that. With this plan you'll also get 10GB of mobile hotspot service, and after that 10GB is used up, you'll be limited to 2G speeds (versus 3G on other networks).
Sprint has put together a nice chart showing how its plan compares to the other networks out there - T-Mobile, Verizon and AT&T. Sprint is still the cheapest, but there are some differences between the four carriers and their unlimited plans. For instance T-Mobile and AT&T do stream video at 480p by default, however those can be toggled off at no additional charge, and stream at its native resolution. Verizon does this at 720p, Verizon also bumps up the mobile hotspot allowance to 15GB from 10GB on other carriers. AT&T offers customers HBO for free, while T-Mobile covers a Netflix subscription up to $10 if you have two or more lines. So each carrier offers unlimited data and each one is slightly different from the other, so it'll come down to which one meets your needs and offers the best coverage. If Sprint coverage is great in your area, 5 lines for $100 is not a bad price at all.