I have been looking at the website of Tim Moss and his Database of Long Distance Cycle Journeys https://thenextchallenge.org/ldcj/.
Looking at the median cost of cycle touring per person which is £450/month/person. Median is better in this case because there are some world record attempts in the database - these people spend a fortune on their trip. If we were to go on a full blown cycling journey without any extra income and work, we would probably run out of money in about 7 years. I would be 40 and DW 37, oops that would be quite a middle life crisis!
So I had a look at the median cost per kilometre from the database, this is £0.31/kilometre. With our current savings and SWR of 0.03 we could cycle ~7250km/year, which is roughly 140km week.
Of course, cycling 20km/day instead of 70km/day will not solve the financial struggles of a long distance cyclist

One way to think about it would be to cycle 140km for two days and then find a warmshowers or couchsufring hosts for 4/5 days. This means free place to stay in exchange for changing out and being socially active (though some hosts just let you be and do whatever you want)
Another way would be to cycle 500km over 7 days and then stay with a helpx or workaway host for 3 weeks. This would mean free place to stay and food in exchange for 10-25h of casual work every week.
Yet another way would be to do a conventional cycle touring trip for about 20 weeks totaling 7250km (to have an idea, this is more or less Edinburgh-Istanbul-Edinburgh, or San Francisco-Mexico City-San Francisco), followed by a conventional employment for about 7 months. In this option, the investments would not be touched, because 7 months of conventional work would be more than enough to finance 5 months of cycling adventure. Where we work now, accommodation and food is provided and the organisation would most likely be happy to have us back. So maybe this is the way to go!