According to this RedFin data from 2019 -- which looked at normalized sale prices and Walk Scores above 50 -- it is about 23.5% or $77,668 for 16 major US metro areas. Again, this is 2019 data and so things may have changed a bit, especially with the whole COVID thing.
It also varies by metro area in this data set. The premium in Boston, for example, is almost 30%. Whereas the premium in Oakland is actually a slight discount (-1.3%). There are going to be local conditions that play a role.
But as a whole there is an economic trend here that makes intuitive sense to me. Though it's not just a question of how pricey your home is. You also need to consider your transportation costs, the value of your time, and the health benefits of living in an environment that promotes consistent and moderate activity.
When you factor all of these things, maybe "premium" isn't the right way to look at this.
I received an email this week from a senior real estate executive who was sharing the fact that, in response to COVID, he had decided to give up driving completely. He was now cycling everywhere -- whether for work or for personal errands. And it was doing wonders for his health and his overall well-being.
Indeed, this feels like some sort of golden era for urban cycling. Back in May I wrote about how Toronto City Council had just approved the largest ever one-year expansion of bike lanes. Some 40 km. When have we ever moved this quickly and without months (okay, years) of painful debate? Probably never.
Of course, it's not just Toronto. This is happening all over the world. Here are some of the numbers (taken from this recent Journal article):
Paris added 400 miles of pop-up bike lanes across the region -- all of which didn't exist before the pandemic - some of the streets being tracked have seen a doubling in usage
Oakland closed almost 10% of its streets to cars
Montreal is adding an additional 70 miles of pedestrian and cycle paths
Bogota is the midst of planning for 47 miles of temporary bike lanes
The UK has fast tracked over $315 million in capital spending for bike infrastructure -- referring to this as a "once-in-a-generation" opportunity
New York's bike share service (Citi Bike) saw year-over-year usage surge 67% in the first 10 days of March alone -- before any shelter-in-place rules were even imposed
There are obvious reasons for this rush to build out cycling infrastructure. We're in the midst of a global health crisis and people are staying away from public transit in big numbers. But I think it's also important to keep in mind that in many / most cases, there is really no other viable mobility solution. You cannot take all the people that used to ride the tube in London and plop them into cars. There isn't enough space.
So cities all around the world are doing the sensible thing and acting fast to make sure that it's safer for people to move about on bikes. But as we all know, humans tend to have a bias toward the status quo. And so when this is all said and done, I suspect that many of these pop-ups will end up sticking around. And that will be a good thing for cities.

This is a map of the Bay Area Rapid Transit network:

And this is an elegant visualization by Ray Luong of ridership levels over the course of one day: February 4, 2016. If you can’t see the embedded video below, click here.
[youtube https://www.youtube.com/watch?v=owGgbAS7Wq8?rel=0&w=560&h=315]
Note how the lines speed up as they go through the Transbay Tube connecting San Francisco and Oakland. That’s actually what happens. Within the 10 km-long tube, the trains reach ~130 km/h, which is more than twice as fast as the average speed throughout the rest of the network.