As of 9:30 - I guess your spreadsheet will be live and therefore subject to change as you respond to comments?

I note the comment re. suppliers, but buying from China - usually the best option - figure on getting stung for import duty especially for big/heavy/shiny items like these.

Those particular stepper drivers need DC so, depending on the transformer selection you might be cutting it fine (by £20 or so) for the rectifier & caps. Unless you've found a suitable toroidal transformer for £50. Hmmm, 36V?, and those stepper drivers?, you'll be compromising the potential performance - but that's a different question to the one you've asked here.

You've completely over-egged your CY cable costs - but that's no bad thing. You can cover the costs of all cabinet wiring and marking with the budget you have.

Oh, What about a cabinet to hold the control gear (+£75)? E-Stop ("oh shit!") button, miscellaneous switches, relays and bases, add £100 (or take that off your budget for the PC). Connectors etc, into the cabinet - add another £60, unless you're hard-wiring everything (I'd not recommend this option!).

You'll need a 24V and 5V supply also. Think if you're using DIN rail and terminals in the cabinet.