OK, Qjump.co.uk wants a login for price details, but I've got one. It's free and spam-free, so far.
Abbadon: 3 - 3.5 hour journey Newcastle-London King's Cross: there're direct trains every half hour or so for most of the day. Saver Return (railcard) £60. Sometimes it's cheaper to go not-on-a-Friday, and after 10am. There may be cheaper tickets that requite you to book a particular seat, eg Super Saver, Apex, etc. Also, single tickets are sometimes cheap: GNER Advance 2 for the outbound is £20.50. The last direct train back on Sunday leaves at 9pm, arrives 0055.
Kan, you're coming from Aberdeen aren't you? That's a longer journey - seven hours. 0955-1701 / 1025-1743 / 1123-1847 / 1225-1926 / 1323-2044 / 1425-2145 / 1455-2218 / 1622-0018 on the Friday. Some are direct, most change at Edinburgh Waverley. Last train back 1500 on Sunday for 2330. Saver Return £71.20 (railcard), singles for (£12.20-27 not available for this example date of 20th Oct as the stupid thing only goes a couple of months ahead) around £27 upwards.
BCLG100 from ... Carlisle (thank goodness for the CFC Frappermap): journey is 3-4 hours, like Abaddon's: every hour or so.
Journey back on Sunday takes twice as long for some reason.
Saver Return £52.65 (railcard), Value Advance Single A is £19.15.
[collapses in a heap, exhausted]