Don’t worry about rebuttal on this one. This battle is already over, but the war is not.
I have much experience as a past consultant and manager of consultants dropping out of the sky into new customers where the shop is die-hard MS or whatever, with my “new” technology to change the shop over. In my scenario, it was always a case where senior management made a strategic choice and we had to “change” the staff to learn, accept, and prosper with our new development environment. It is slightly different than what you have since in my cases it was always a management mandate, but hear me out. It doesn’t matter if it is management or the developers themselves that resist, the problem is how to address the resistance.
Tools/languages are a religion, but more importantly, they are sometimes all a person knows and they do not want to take on the risk and effort to change an entire department. It is a lot of work. They will resist until the end of time. They also may enjoy golfing with the MS sales rep and don’t want to give up the free days at the country club. Sometimes you will never know the underlying resistance as it may be hidden.
I found it always best to PROVE the new technology. Estimates are voodoo numbers and easy to be discounted by either side.
PROVE RoR by offering to develop a small prototype in parallel or sequentially to an identical effort in MS technologies (it can be a made-up project). Make the duration 1 week each (or 3 days, whatever). Present the results after the experiment is over and offer sincere benefits and drawbacks of each. Offer to do it in off-hours if you have to.
Do not do the experiment in a vacuum. Be very inclusive of the opposing parties, making sure they are involved in the process. They fear what they are unfamiliar with and this is a way for them to dip their toes in to the waters. If you work in your cube alone, the “two sides” separation will be perpetuated. Get someone from this manager’s team to participate with the 2 of you working side-by-side on Rails prototype and then follow it up with the 2 of you working the MS prototype. This person will be your messenger. Your message will always be self-serving in their eyes.
In every case, I had to win over the religion by letting the opposing side see and experience the benefits first-hand. Success, confidence and results talk; estimates do not, especially those delivered by someone who will bring a natural bias to support their desired outcome.
Failing the above, get your resume/CV together and go to a company where you don’t have to fight a long battle. There are many shops where you’ll be able to focus on the business problem and not the technology selection.