£120 is the cheapest option
The price can vary enormously depending on when you are travelling but a single ticket could be about £115 and a return not much more.
These days all rail travel in the UK is very variable in price, depending on how far in advance you can book and the time of day at which you can travel - avoiding rush-hours is cheaper. Best to look...
From where to where? be more specific
You'll get a train from Glasgow Central to Preston, change there for Blackpool.