If you're really looking for something affordable there is a limited stop express bus (
number 702) that currently has a flat fare of £2 (government subsidised). It serves a number of stops in Slough including one about 5 minutes walk from the train station and it goes to London via the M4 motorway. In London it has stops at Hammersmith, Kensington, Hyde Park Corner and Victoria.
About 15 years ago I used it to commute 5 days a week from Slough to central London, however:
- I was living about 30 minutes walk away from Slough station but only 5 minutes walk from the bus stop for the 702
- at that time the M4 motorway had bus priority, which was important in the morning peak, but that has since been removed
- I was working near Victoria, so the express bus took me all the way to work
- the frequency of the 702 bus is much lower than the train (but it is commuter-oriented: departures from Slough at 05:40, 06:09, 06:44, 07:04, 07:53 in the morning peak but it reduces to roughly hourly after that during the day)
Since your workplace is in Farringdon, if you use the 702 bus it would only cost you £4/day in bus fares but it would not take you all the way to Farringdon.
If you got off the bus at High Street Kensington, however, then you could take the London Underground to Farringdon for a further £5.60 per day (you'd take the District or Circle line to Paddington and then the Elizabeth Line from there to Farringdon - you would need to use an Oyster card or a contactless payment card for this and it would count as one journey for fares purposes even though, if you follow the signs, you'd need to tap out and back in again at Paddington when changing lines there). Other possible transfer points between the London Underground and the 702 bus include Victoria, Hyde Park Corner or Hammersmith (but Hammersmith is in zone 2 so your journey from there to Farringdon would cost a bit more).
I'm just offering the above as a cheaper option. To be honest I think it would be pretty gruelling to take that route 4 days a week as, while it can be surprisingly fast if traffic is light, it's never as fast as the train and it can be agonisingly slow at times. Whether it makes sense for you or not may depend where in Slough you'll be staying.
It is a very cost effective route, though. I'd say it's at least worth knowing about this route as a low cost alternative in the event of serious disruption, train strikes or any days when you need to travel off-peak (when traffic is lighter and trips by express bus are quicker).
I hope you enjoy your time in Slough! Please don't be rude about it - it's where I grew up and I'm still rather fond of it.