You don't need 100Mbps, so you could step down to 25Mbps. However, for the $10/month difference, maybe your internet usage is worth the extra? And if all 3
TVs might be in use at the same time (streaming different things), that might further support paying the extra $10.
Comcast where I am runs promotional pricing specials on broadband-only offers. If it could work for you, perhaps cancel, wait a few days, and then contact their sales department to see if you can sign up as a new customer and save some money for what is usually at least a 12-month promotion. In my own case, I'm NOT paying $85/month for fast Comcast broadband plus Comcast voice... and I've been on for much longer than 12 months. At the end of a promotional period, call up and threaten to drop the service and you may be able to talk them into finding you a new promotional deal (still lower than $85/month). Of course, if you have no viable competitor in your area, this tactic may not work.
Take note if Comcast enforces a bandwidth cap in your area. Video burns a lot of bandwidth and 3
TVs playing a lot of streaming video could really eat it up. If you hit the cap, they'll typically upcharge you and that can get expensive.
What services you need can only be answered by identifying the programming you desire and then looking through the various services to see which- or which combination of services- can deliver what you seek. For example, if you actually watch 10 channels of the 220+ in "Digital Preferred," then you look for the service that delivers those 10 channels.
Perhaps there's only a show or two on a channel or two in your desired channels list? If so, then maybe you don't need to seek out that channel but look to iTunes or similar and buy season passes to just that particular show(s)? That's how the cord-cutting mentality works... a game of how low can I go on cost by pinning down how to get what I want from 1+ streaming & VOD services. In many cases, this works by being willing to hop app-to-app or even box-to-box to get all that you want for as little cost as possible. Of course, then you have to train the family on hopping app-to-app and box-to-box vs. the old way.
Also note that most of the highest-rated programming is still on the core networks of ABC, NBC, CBS, FOX and CW. If you live close enough to a city, a good old antenna can get you up to all 5 of those at the highest resolution (better than streaming or cable/satt) for no monthly fee. Check your address on antennaweb.org and it can give you a sense of how many of those you can get. In addition, such local broadcasters sometimes also have some good classic TV channels such a ME-TV, LAFF, AntennaTV, Comet, Grit and various others. I find myself watching a fair amount of ME-TV & LAFF for free via antenna. There are hardware options that can flow those to your AppleTV (see stuff like the HD homerun boxes
https://www.silicondust.com) or consider a TIVO Romio OTA DVR
https://www.tivo.com/shop/ota-detail for the local channels, which can be an especially good option if many of your favorite shows, sports & news are available via the locals over-the-air.
Your "what are the costs" question is tied to which service(s) you choose. Pricing is pretty readily viewable as you explore the various options.
Last I heard, the Netflix offer that most people associate as Netflix supports 2 simultaneous streams in a single household. If that's still the case, you probably can't stream 3 different shows from Netflix to those 3
TVs without paying more for an upgraded "premium" subscription and/or having 2 subscriptions. However, check with Netflix to see if my memory of that particular detail is right or wrong. Edit: here's their plans, and you would need "premium" for 3 separate streams:
https://www.netflix.com/signup/planform
Be sure to use free trials of the streaming services before committing. There ARE shortcomings/tradeoffs to all of them. For example, if you like Dolby Digital 5.1 surround, NONE of them offer it- just stereo or mono sound. If you like full DVR functionality, several offer software DVRs but they tend to be feature limited with issues like having time limits to watch a saved show and/or no ability to skip commercials. Again, use trials, thoroughly test stuff you take for granted with what you have now and then make a good decision based on such compromises.
In my own case, I continue to watch the streaming options but cling to DISH at the $49.99 price lock offers. One on-screen guide for all programming, no programming delays vs. first run, a real full-featured DVR, Dolby 5.1 audio, Dish Anywhere app to stream to iDevices, all of the live sports channels I desire, integration of the local channels right into the same on-screen guide (and recordable on the same DVR), no Comcast broadband cap issues, and so on. I can't seem to spot a streaming service or combination that gives me all of what I want for less than that.
I will point out that at least where I am Comcast offers double & triple play combos that seem to be targeting a bill in the $80-$100/month range. For example, Comcast Cable + Broadband + Voice for $90/month as a bundle. If you are generally happy with what you have, you might want to compare the potential change vs. such bundle offers. I suspect what you are facing for Broadband only can get you broadband + cable for the same money (or maybe a little less).
I hope this is helpful.
