The new campaign/investigator sets would be the cheapest. Some scenarios are really hard to find even in English. On a budget i would recommend the investigator set for dunwich as it really fleshes out a lot of the classes. Together with the card from the old carcosa deluxe it should allow for some decent deckbuilding. I would also suggest using the playercards from the Dunwich deluxe box as proxies for cards you really want to use in your deck from later sets. That way you have playercards for a long time while you get the new complete campaign in release order.
If you want some more playercards after that the starting investigators are quite good value.