There is no cheap and quick way to get from Lagos, Portugal to Santander, Spain. It practically impossible to do the trip cheaply in one day.
The following to me seems to be the best option:
Train:(Daily)
20h16 21h55
LAGOS: 20:16
FARO: 21:55
Change trains at Tunes Junction.
Price: € 12:85
Earlier train at 19:15 - Price: € 6.15
Walk to Faro Bus Station.
Bus: (Daily) (operated by www.alsa.es)
FARO: 01:45
SEVILLA: 05:45
Change bus:
SEVILLA: 09:30
SANTANDER: 22:00
Price: € 49,32
Have a look at this recent article on my blog which will give some explanation although it pertains to doing the trip the other way.
http://barlaventostravelblog.blogspot.com/search?q=Santander
