You're right that there are lots of elaborate and expensive sets, but the basics are still available.
E.g. you can still buy loose bricks from LEGO, so can make it as simple as you like. If you want basic stuff packaged up, the LEGO Classic line has sets starting very small that consists of a batch of bricks and a small set of themed special parts. On the UK site at least they also have more than 500 sets under 20 GBP/25 USD (you can search by price) including a number under 10 GBP / $12, but the majority of these sets will be full of special parts simply because there's little point in packaging up the same small selection of basic bricks in umpteen different sets.
Overall, the price per piece of LEGO varies greatly by set (average per category of set varies from less than 20 cents to nearly 2 dollars per piece) because of different weighting of types of pieces, but the inflation adjusted cost of the basic/cheapest pieces have remained consistently stable [1]
E.g. you can still buy loose bricks from LEGO, so can make it as simple as you like. If you want basic stuff packaged up, the LEGO Classic line has sets starting very small that consists of a batch of bricks and a small set of themed special parts. On the UK site at least they also have more than 500 sets under 20 GBP/25 USD (you can search by price) including a number under 10 GBP / $12, but the majority of these sets will be full of special parts simply because there's little point in packaging up the same small selection of basic bricks in umpteen different sets.
Overall, the price per piece of LEGO varies greatly by set (average per category of set varies from less than 20 cents to nearly 2 dollars per piece) because of different weighting of types of pieces, but the inflation adjusted cost of the basic/cheapest pieces have remained consistently stable [1]
[1] https://brickinsights.com/statistics/ppp