[Closed] Commuting Train Station Station Bike

So I've got myself a new job to which I'll have to commute to by train because it's too far (for me) to cycle.
I have a 4 mile ride to the local train station where I'll have to lock my bike up for the day until I return, I've been commuting on my hardtail but had somewhere safe to lock it up and don't feel comfortable leaving at a train station all day so I'm looking for something else.

Requirements are mudguards, panniers/rack for my rucksack, quicker than & worth substantially less and wouldn't be as attractive to a thief as my other bike. I'd also like to enjoy the ride, on something half decent that doesn't weigh a tonne, not fussed by looks as long as everything works well, I know some people will find that statement kind of defeats the object tho.

I don't want to buy new because I think a shiny new bike in the racks would be more likely to disappear rather than a already loved bike, even if it was a cheap one.

Should I be looking on ebay for a whole bike and trying to sort it myself to suit or build it from the frame up using used parts.

Also I'm concerned that having a large Kryptonite S4 D Lock might make any bike look attractive/worth pinching to a thief, but obviously it would keep it more secure (I hope) than a £15 Argos jobby.
Any other advice would be great & thank you for listening to my ramblings!