-
The best way is to find some in a skip, as happened to someone on here a while back, but I can't remember who it was.
If you want a large set, you will probably spend an arm and a leg. Then again, you could spend all that LEGO time watching discounts. :)
I'm sure there are good deals on job lots in the usual on-line marketplaces, but I never go near those.
If you want to buy new and just want LEGO, rather than sets (and remember you can download all of LEGO's building instructions from their site), I'd say this is currently a good deal (I've linked to it before):
It may contain colours you don't want, but it's quite a lot of stuff for the money, certainly way cheaper than sets.
Other than that, Argos occasionally do quite significant discounts of around 40%, and other outlets sometimes up to 33%, but usually just 20%, which I think isn't really a discount. You could sometimes get stuff at half price in LEGO shops, but I haven't seen that for some years.
LEGO, unfortunately, has always been overpriced.
-
Adding to what Oliver said; keep an eye on here.
Whats a good way to get some reasonably time consuming lego without spending an arm and a leg? Is this a fools errand and not really a thing? Just want some stuff to make and keep myself busy while housebound with a newborn.