Frkl

Check out the C&V thread on drop bar conversions for mountain bikes. There is a lot of info on "modern" parts there too. You will see that it can either be simple or a nightmare, even if you have lots of experience. I have done this several times and it often involves digging deep in the parts bin. Even if you start off with a detailed list, you will most likely need other parts. There are little things that cause unexpected problems.

But it can be a great learning experience!

You can simplify and reduce costs by going 1x, just reuse your crank with a new chainring. But you may need spacers to adjust the chain line

One option would be to get a Microshift Advent set up, which comes with a wide range cassette, derailleur and brifter (other styles of shifters are also available). It costs something like 150 for the package. I've had good experiences with other Microshift products.

But I wouldn't do this because you think you will save a lot of money. You might, but probably not in the end... In my opinion, it's worth it if you have a super nice frame to repurpose or if you get a kick out of problem solving problems that you created for yourself. I do

Edit: another thought, you could try any number of alt bars if what you want is hand positions. They take flat bar 22.2mm shifters and brake levers, usually. Like the Surly Corner bar, or take an Albatross style bar, and flip them.