In 2025, I traveled by bus in South America, starting in Lima, Peru and ending in Rio de Janeiro, Brazil. Here are some details for anyone interested in doing the same.

	Leg	Start	End	Company	Date	Depart	Arrive	Distance (mi)	Duration (hh:mm)	Price
1	Lima → Arequipa	osm	osm	Cruz del Sur	5/23	2:30pm	8:46am	619	18:16	$35.50
2	Arequipa → Puno	osm	osm	Cruz del Sur	5/29	1:50pm	8:55pm	184	7:05	$15.04
3	Puno → Copacabana	osm	osm	Titicaca	6/2	6:45am	10:50am	88	4:05	$7.43
4	Copacabana → LaPaz	osm	osm	minivan	6/3	2:30pm	6:45pm	90	4:15	$7.29
5	La Paz → Uyuni	osm	osm	Todo Turismo	6/13	8:15pm	7:45am	336	11:30	$41.84
6	Uyuni → Potosí	osm	osm	Trans Quijarro	6/15	12:00pm	4:20pm	127	4:20	$5.83
7	Potosí → Sucre	osm	osm	Trans Emperador	6/19	12:15pm	4:30pm	97	4:15	$4.37
8	Sucre → Santa Cruz	osm	osm	Flota Capital	7/5	3:50pm	3:45am	301	11:55	$25.36
9	Santa Cruz → Asunción	osm	osm	Stel Turismo	7/16	7:00pm	4:20pm	847	21:20	$123.91
10	Asunción → São Paulo	osm	osm	Expreso Paraguay	8/8	7:10am	7:05am	858	23:55	$67.83
11	São Paulo → Rio de Janeiro	osm	osm	1001	8/27	9:30am	4:20pm	267	6:50	$19.98

Notes

Route: As you can see in the map, this isn't the most direct route from Lima to Rio. A more direct route wouldn't go through Puno and wouldn't go into southern Boliva - Uyuni, Potosí, and Sucre. But if you're in the area, all of these are very much worth going to!
Prices: Prices are converted to USD at the approximate conversion of the time. All the tickets bought in Bolivia should probably have an asterisk: at the time of travel there was an official and unofficial exchange rate that could differ by up to a factor of 2. Things bought with a Visa credit card were much more expensize than using cash (if done via Bank Transfer).
Difficulty: Everything was straighforward and easy. Like most of Latin America, just find your way to the bus terminal and you find frequent buses almost anywhere. I read reports of a bus-ride-from-hell across The Chaco, but beyond being long (and too not much scenery), it was a comfortable ride to Asunción.
Safety: My main safety concern was riding buses in the mountains of Bolivia. If you do some Googling, you see too many reports of buses crushed after falling off the side of cliff in the middle of the night. For that reason, when I had the choice, I opted for the slightly more expensive option in hopes that they have higher safety standards.