Buy Elite: Dangerous Lifetime Expansion Pass
Lifetime expansion pass includes:
If you buy all you can now separately then you will "save" 50 pounds (130-30-10-40 = 50) but only have 1 expansion tied to your pilot. Now price equals to what you will have to pay for the game and 2 expansions, all above that will be free.
Note: if you already own the game then sadly you can't buy only lifetime expansion pass as it's not sold separately, so you will "lose" 30 pounds, basically it means that you will pay similar amount as for 3 expansions and anything above that will be for free.
Past
Long time ago to receive same you would have to spend: 35 for game +15 for beta + 35 for lifetime expansions total of 85 pounds, so now difference is only around 1 expansion price but you already can play the game and see that there is no risk to invest that couldn't be said when game was on kickstarter.
Present
This year alone we will have 5 major updates and first expansion. So far we had major updates like Wings, Power play and next week we will play Close Quarter Combat.
Future
So we can easily expect total of 4-5 expansions in years to come as Elite: Dangerous will be updated frequently for next 7-10 years with new content and new game play mechanics.
Expansions are not regular DLCs or updates – they will introduce to players completely new game play:
Expansions are like completely new game with unique and otherwise inaccessible game play elements, locations, items and other activities.
Yes, you can't compare different games, because many are unique and one of a kind, but still, to better understand the prices i will do that. Keep in mind that Elite:Dangerous has no subscription fees and no microtransactions involving in game items (only cosmetic items like skins can be bought), so frontier only would have income from sold game copies to cover all expenses - servers, salaries etc. And as they are against monthly fee option paid expansions seemed like a good idea, i will not judge them because that is their preferred style of conducting business but just compare with some other games to show you that in the end it's not as crazy as it sounds.
Elite: Dangerous 5-10 years life span: 130 pounds = 1-2 pound/month.
Witcher 3 – 60 pounds (with DLCs): 1-3 months = 20-60 pounds/month.
WoW – 9 pounds/month or 108 pounds/year.
Eve online – 7 pounds/month or 84 pounds/year.
If you have fun with Elite and return to play it after other games (which, let's face it, in most cases are just one time games) then you must consider buying lifetime pass, just because it will cost you less in long run, but if you play Elite only occasionally and are still bored then better wait to see exactly what is inside each expansion before buying it.
And if you don't like Elite at all then you already know the answer - the game is not even worth single pound, so don't bother, simple as that ;)