Cheapest way to visit London on the 20th of June from Dundee?

I’m currently trying to go see Gorillaz in London because I don’t want to miss my chance after my first concert went terribly, but I’m a student who’s never once planned their own trip. I’m looking for a way to travel down and stay for one night at least without breaking the bank, as I don’t have a lot of money. I have OCD, so I’ll need an en-suite bathroom at whatever hotel I stay at, and it would be a trip for two. What would be the lowest price I could pay to do this? My total budget is around £250. I’m willing to go through any means of transport and stay at any hotel that would give me an en-suite. I’m unsure what the “provide two options” part of the low effort post rule means, so I’m sorry if this doesn’t meet the criteria.