What is the cheapest way to travel long-distance across the UK?

I live in London however I am hoping to meet a friend in far northern Scotland (Wick) in October / November, but not sure how to get there cheaply.

I'm a student and this is a one-off experience however I don't want to be spending loads, and where they live is in a very obscure location far from any of the major cities.

I did a quick look with split ticket however no itineraries found. Lots of train finder sites have very split prices ranging from over £100 to £25 (though I am not sure to trust it). I found a Google transport planner which found something for me however the links didn't work.

Any places that can help me plan to a fixed location and check tickets across multiple different modes of transport? I'd preferably not like to use road for anything more than 4h.

This will probably be booked in short-notice, however this can be changed if time is necessary for price