Hi Joana,
Thank you for those details. I think I can help quite a bit. I hope I’m right to assume that you have either a 16-25 railcard or a 26-30 railcard? If not please let me know because it may change some of this.
So, firstly for Wembley Park I recommend travelling from St Albans to Hendon on Thameslink, then get out and take bus 83 towards Wembley Park station. The bus takes around 20 minutes but easily beats the train doing Hendon – West Hampstead – Wembley Park which is a lengthy double back. It’s even worse if you go to St Pancras. A railcard discounted off-peak day return from St Albans to Hendon is £7.10, plus £1.75 x2 for the bus – total £10.60.
For Southfields there are some options depending on how long you want the journey to take. The fastest way is St Albans to Blackfriars on Thameslink and District to Southfields from there. That’s £18.10 for Thameslink plus £3.80 peak single and £2.05 discounted off-peak single for the District – total £23.95.
Splitting at Hendon requires taking the stopping trains and potentially waiting 15 minutes at Hendon for the next train after you’ve touched the Oyster card in (or out on the way back). You’d then need the Anytime day return from St Albans to Hendon which is £12.75, plus £6.60 peak single and £3.55 discounted off-peak single for Hendon to Southfields via Blackfriars – total £22.90.
For a bigger saving you’ll need to take 4 trains. St Albans to Hendon, Hendon to West Hampstead Thameslink, West Hampstead (Overground) to West Brompton and West Brompton to Southfields. That will be £12.75 as above, plus £3.60 peak single and £1.95 discounted off-peak single for the other three trains combined – total £18.30.
Now for the long day. Start with whatever is your preferred journey to Southfields. Once you finish there take the District to West Brompton, Overground to West Hampstead and Jubilee from West Hampstead (Underground) to Wembley Park. It’s not as bad as it sounds and costs just £1.45 discounted off-peak single. Then it’s the bus to Hendon and use whichever return ticket you bought in the morning to get back to St Albans. It doesn’t matter if the ticket was to Blackfriars, you can still use it only for the Hendon to St Albans part in the evening.
So £18.10 + £3.80 + £1.45 + £1.75 = £25.10 to go fast to Blackfriars,
or £12.75 + £6.60 + £1.45 + £1.75 = £22.55 to split at Hendon and via Blackfriars,
or £12.75 + £3.60 + £1.45 + £1.75 = £19.55 via Hendon, West Hampstead and West Brompton.
Finally for Saturday it’s off-peak all day, plus you can buy cheaper super off-peak returns from St Albans which are only valid at weekends. St Albans to Hendon is £5.90 day return while to Blackfriars it’s £8.15.
So £8.15 + £2.05 x2 = £12.25 fast via Blackfriars,
or £5.90 + £3.55 x2 = £13.00 split at Hendon via Blackfriars (NOT WORTH IT),
or £5.90 + £1.95 x2 = £9.80 via Hendon, West Hampstead and West Brompton.
Other things to note. The tickets from St Albans are all railcard discounted. Everything else is on Oyster and is disounted off-peak but not peak or for the bus. I assume you return from Southfields outside the evening peak 1600-1900. The three stations at West Hampstead are very close together taking no more than 5 minutes to walk between any two. If you change at West Brompton you MUST touch the pink reader in the passage way between the Overground platforms and the District line platforms.
I think I’ve covered everything, but do come back if you have any questions.