We arrived in Toronto total novices at the Presto Card, had some apprehension that evening how much to load on it, had one technical glitch with it on the first full day, but left there as experts. Jishnu discovered that I missed an important fact about the Presto Card, namely that when used on TTC (streetcars and subways -- and buses if we wanted to ride them), one gets 2 hours of riding per swipe. So it would not have been C$3.10 per segment. This also rendered the C$13 Day Pass as too expensive since we could get more bang for our buck out of the C$3.10 . Also, on Thursday the entire run from lunchtime when we entered the Line 3 rapid transit at Scarborough, until final arrival by the 510 streetcar into Union Station was on one fare; we had remained in the paid areas of the system all afternoon. And on Wednesday, we also did our entire riding under one 2-hour period because we ended up not taking the last planned subway segment to Union Station but instead walking from the streetcar to dinner.
I updated our Transit Costs page for TTC Wednesday & TTC Thursday, based on our actual travels, and the above facts. Note that particularly on Thursday, the per-ride costs come way down thanks to remaining in the paid system for so long.
Having loaded C$108 dollars initially on my card, I ended up with C$2.49 left on it after its last use (and without having to add any more) before leaving Toronto for good. Roughly US $1.90 for a souvenir.