Car loan? The bus is cheeper and you can have a sleep on a bus. And you can buy a decent car for under £2000 (mine was exactly £2000) if you really need one and can't use the bus. And yes, a normal photographer should be able to afford one a big white. For some it'll be nothing, for me I can do one a year, for others it might take three years. But for a wildlife shooter you are likely to have more than one and it shouldn't be unthinkable on a forum full of photographers that that is an expectation. Especially not in a thread about these lenses.
Normal wage here starts at £18,000 to £26,000 per year with £500/month to rent for a 2-3 bed house, £160 council tax, and £200 to food, with £120 covering 4 weekly bus passes. A photographers wage should be way higher than that I should hope. The normal monthly expense for a person is £1000/month assuming they are living alone in a 2 bed house.
£300-£500 is normal. Pushing sub £400 more often if the house is brick instead of stone. You can buy a stone house for anywhere over £200,000 or a brick built for anywhere from £40,000 to £150,000 depending on how bad the area is.
Okay so this is wildly off topic but I have to point a few things out, as I live in Scotland but most forum members don't, and may be swayed by your statements. Your original suggestion that an average photographer could afford a ~£10k lens
per year was silly, and you're massaging the figures even as you pull back from it (next it was 'not just once in a lifetime'!). You've ignored income tax, national insurance, and a whole host of other living expenses - phone? Internet? Clothing? A computer to process your photos? Even then, rents are considerably higher than you state - I've just checked and the average for a 2 bed property is only just under £500/mo in a handful of postcodes, most are much higher, and for a 3 bed, far higher still. Buses don't generally take you where a big lens is useful - trust me, I've spent years doing wildlife photography without a car and public transport doesn't tend to go where the birds are (or at the best times for them); it's not impossible, but seems an odd choice if you're also saying a car is affordable (but once again, you've missed off insurance, road tax, fuel, maintenance, etc). Living alone is more expensive than sharing, btw, as some costs are fixed.
Any £10k+ purchase is a big, rare thing for almost everyone, and when it is non-essential, as these lenses are for even the vast majority of photographers, making it sound casual and easy is ridiculous. Saving £100 a month (which is a lot on a modest income!) it would take over
eight years (although in any case I suspect more people buy them on credit and pay it back over several years, rather than saving up). Let's be realistic. (This is why the budget super telephoto lenses are so important - far far more people can justify a £1000 lens even with numerous compromises).
I have 1 supertele and couldn't justify getting a second one. Most wildlife photography enthusiasts I've known have at most a couple - the 100-400 and a long prime, say. I would say only the very richest hobbyists have several (not counting people picking old models up secondhand, but even that is expensive).