Recommend for cell phones in Taiwan - prepaid, rental, buy

Hello all.
I’m coming to Taiwan for a short trip (3 weeks). When traveling in the US, it’s convenient to have a cell phone - and you can buy a cheap Tracfone at Walmart for $20 and add minutes to it buying pre-paid cards in small increments ($5, $10, etc). All very inexpensive.
Is the same thing possible in Taiwan? I don’t want to purchase a fancy phone or get into an expensive rental. I’ve seen ads on the Internet for $70 for three weeks rental, and SIM cards for $100. I just want a cheap (nearly disposable) cell phone. Any recommendations?
Thanks very much !