£10 but I also had a free £10 off a mate to use as well because of their referral.
Some of the players above I've bought have seen a very good increase in their stock.
Ben Chilwell - £1.71 to £1.93 (22p)
Kasper Dolberg - £1.60 to £2.06 (46p)
Angel Gomes - £1.59 to £1.82 (23p)
Leandro Trossard - £1.13 to £1.42 (29p)
Hakim Ziyech - £2.22 to £2.63 (41p)
Marc Roca - £0.74 to £1.23 (49p)
Roca & Trossard were tips from the person who referred me to the site.
Regarding stability, I'd say purely depends on who you buy. Younger players with potential could be goldmines, but if they have a few shit games or aren't 'flavour of the month' and the attention in the media dies down, their stock might fall a little.
I got quite lucky with Chilwell as I got him before there was talk of him playing for England. I wish I did the same with Maddison though as well.