score:5
I suspect you're correct; Taoyuan station to Taipei station is 52 TWD by local train, or about US$1.60.
There is also the recently opened Taoyuan MRT Subway service via the airport, but this doesn't cover the old Taoyuan station (only the new HSR one) and is much pricier at 160 TWD.
Upvote:3
If you get a "normal train" a PuTong (Kuai) ticket from Taipei main station to Taoyuan station the price is 31 Taiwan dollars. You may be allowed to board any train with this ticket but legally you are only allowed to board the slow train that stops at every stop.
The answer is $31NTD on a stopping service.
Go to this website to check.
EDIT: actually, looking on the website shows that the putong kuai train left service in 2020 except for selected tourist routes. the next cheapest train would be the qujian or qujian kuai (fast) train at $42 taiwan dollars for an adult and $21 twd for a child or pensioner.