Tere, I'm a Serb living in Estonia.

Price wise: in Estonia decent houses are 200-250K right now. You can get for 50% of that in Serbia. But, if you're going very rural, unlikely you'll find a decent house for sale, more likely you'll have to build one yourself. Which can be a bureaucratic nightmare tbh. Bureaucracy in Serbia is a far cry from Estonia, it's a battle that might take months, and even years.

Soft rural living: these are villages typically further north, with 1-5K inhabitants with solid density (you'll have neighbors nearby), not too far from a city. Decent peace and quiet, nice scenery, and decent infrastructure.

Hardcore/real deal rural living: usually in southern parts. Amazing peace and quiet, beautiful hills/mountains scenery, heaven really. Usually very few inhabitants and low density. But, infrastructure can be almost non existent. Biggest problems being the internet, long drive for groceries, and possible full or partial isolation during snowy months(no road maintenance).

As for people, Serbs are generally open to foreigners, especially ones that are actively trying to integrate and learn about the culture. As with any nation, you'll encounter good and bad people. Some older folks might not have much patience for trying to communicate with you because of language barrier, some will be delighted to see a foreigner fascinated with serbian village life. Young folks almost all speak english, so no problem there.

One important note: Serbia is struggling with air quality last couple of years. It gets very bad during peak winter months, when heating is at 100%. And it is unlikely this will get better for foreseeable future, unfortunately. Investigate a place you want to build/buy for air quality history, as this might significantly impact the quality of your life. If you have a polluted city close by, air travels fast to the surrounding countryside.