I object to having to spend money on shoes and suits that i would never otherwise wear.
My sentiments exactly. In the past tense now in my case, fortunately. My old work togs are now used for gardening/lawn mowing duties. I cut a dashing figure behind my Honda Izy easy-start.
I too was once in IT and it was kind of expected/to your own advantage to keep your skills fresh - this meant personal spend that one of my employers sometimes reimbursed, the rest didn't. I guess they argued/relied on IT bods being sufficiently interested in or motivated by the subject to make it more of a hobby than an occupation. I never played that game, even when self employed, and am now out of IT. Whether the two are related, I'll leave for you to decide!
I once fancied the 'job' of research, but when I did my degree (as a mature student) I realised there was no such thing as your own time if you were in research. That made me scratch that as a job prospect. You really have to love your subject, be consumed by it, so I can see their is no work/personal budget division.
I think the only personal expenditure I had for work purposes (outside commuting costs obviously) was ink, or pencils leads. I liked to use either a fountain pen or propelling pencil for writing (I was old skool in IT; I used to hand write précis code, schematics, system flow before keying anything in) but that was my choice and I never even thought of asking the boss to sign off on the company coffers.
So I guess the answer to the OP is, in my case, about a tenner a year!