I would do one light but I like symmetrical and may try one as a helmet light if two on the bars is too much. I guess cheaper is good but since I haven't a clue what the differences are among them all it wouldn't make a difference to me.
I came across this: https://budgetlightforum.com/t/-/939 and the reviews seem good. The price isn't too bad either: http://www.kaidomain.com/ProductDetails.aspx?ProductId=11097
Does the community have a preferred battery and charger?