It's not about the initial cost of £2K or whatever. It's about long-term costs.
My two (I foster but won't count them for this quick outlay of costs) cost me about £300 a month. That's a 10 year old female cocker spaniel and a two year old male Goldie.
£120 on food - Butternut box and raw food, includes treats.
£90 - Insurance. £60 for my girl, £30 for my Goldie
£20 - Entertainment for them. This includes new toys (Goldie is a destructive little turd), mind games, crafts to create my own mind games for them etc.
£40 - Grooming for the girl.
£30 - Worming, flea medication, vaccinations etc
In terms of long walks, that's great. But you also need to consider your dogs mental stimulation - will it be left alone all day (If so, don't get a dog), will you have time to entertain it and provide mental stimulation etc.
FWIW, my girl is 10 (nearly 11). She still goes for 2 hours a day on walks, plays all day and is constantly needing mental stimulation - she's more energetic than my Goldie. She's not even a working line - she's show, so should be less manic.
Some dog breeds are more expensive than others and you should expect to pay more for a puppy from fully health tested parents. I paid £2.5K for my Goldie but that is because his scores, his parents scores and his lineage is excellent - I couldn't have done better tbh. But I paid £800 for my cocker (admittedly a long time ago).