Bought my AT 7 years ago with 60.000 on the clock. Changed the rectifier (yes for this you have to take the sidecover and the bench off, 2 screws), modified the gas pump (insert a diode for 10 cent), put new front springs, changed the main spring and off we went for another 100.000km. 65.000 during our last trip through NZ, SEA and Australia, riding every day for 22 month.
Maintenance in 2 years sand in AU, mud in Laos, potholes in whole SEA:
every 10.000 km a oil change
1 x new chain and sprockets
new tires from time to time
new breake pads (should change the brake fluid, but didnt)
1 x new brake disks
We went 2up, 450kg. Our bike WAS and IS
In Germany you can find still a lot of them from 200X models (4-5000EUR!) to RD03´s for much less. An RD04, 1990 you can get for less then 2000EUR I guess. If you go for the middle e.g. an RD07, 1993 you can find them around 3000EUR (mine was a 1993 model, with Touratech Zega panniers fitted and a modified bench and I paid 3000EUR). 3000 EUR ready to go around the planet. Fine for me...
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Ps.: In the end of the day it doesn´t matter which bike you take. We met all kinds of bikes, Scoter through the stans, Push bikes in the middle of newhere, some Teneres, some Beemers, Ducati, Goldwings, 50cc to 1500cc. All made it. The main thing is: "JUST DO IT"....