Mostly-unlimited-data SIM cards for US citizens going to the EU?

My guess is that you will not find anything close to what you are looking for. 30GB is a huge amount of data to be using in 15 days, and $200 is a very low price for it. The only way you'll get close to any form of unlimited data would be to sign up for a new contract with a local telecoms provider in each country you visit. Not only would this tie you to three long-running contracts, your data speeds are likely to be throttled after the first few GB you use, possibly back to 2G, which is slow even for looking at emails. This is without even researching whether there are daily reasonable useage limits, which there probably are.

The closest solution that I can come up with that will fit your needs would be to buy an international data SIM card from Telestial.com. This is a US-based provider of international SIMs, so these SIMs will work in all your destinations and you'll be able to have your SIM (regular, micro or nano) delivered and activated before you travel. All these SIMs are pre-paid, so it is impossible for you to go over your limit and be charged ridiculous overage fees. This ticks most of your boxes.

The remaining issues are the amount of data and what it costs. They don't do 'unlimited' and it seems their maximum limit is 1GB at a time. Obviously, buying 30 x 1GB bundles is going to get expensive, so you're going to have to improvise. Hopefully, your hotels will have free WIFI, and if they do, let this do as much of the heavy lifting as you can. I'd also consider dropping into an internet cafe for transfers of large files; a short visit to a hardlined connection will be cheaper and quicker than attempting to do it over the air.

Good luck!

I got fed up with getting a new phone number every time I crossed a border, and so I got Google Fi. Phone calls inexplicably don't work occasionally, but usually the second try works. It also doesn't do everything advertised, but it's still worth it to me to have friends and family know my phone number. Currently, ten US dollars per month to have it, plus ten US dollars per cellular gigabyte, no charge for WiFi. These rates allegedly do not change in any country.

Phone calls no extra charge via WiFi or in USA. Otherwise, depends on location. Ten cents per minute from Spain to USA.

The worst thing about it is not the flakiness, but the fact that I had to buy a specific model of phone for it to work. But they claim that I can order a second SIM and it will work on another device. However, I already get my SMS on the iPad without their second SIM.