Summary: $5/month, $10/month, and $25/month plans with Republic Wireless -- worth checking out as well!
Details: You do mention that Republic Wireless' "plans are certainly cheap" but you don't list details. You are comparing plans that offer a large amount of 4G cell data, so that is understandable. However, it is very noteworthy, in my opinion, that for a plan that includes unlimited talk and text over cell (or wifi), and unlimited data over wifi only, you pay only $10/month! Also, unlimited talk, text, and data over wifi only (a good option to consider for those with wifi at home wishing to drop their landline), is only $5/month! Even unlimited everything (but 3G data speeds only) over cell is only $25/month! On the downside, they do use the Sprint network, which has less coverage than a few of the others such as Verizon and AT&T, so I have read.
Note: I do not work for Republic Wireless or get any benefit in any way from this recommendation. I am a happy $10/month customer using a Moto G; so far, I can highly recommend RW. And: I got my phone refurbished off eBay, for a good deal less than new from RW, and love it. I simply want readers to be aware of all the RW options. Read more reviews; "your mileage may vary"; other providers might offer similar deals.