I need a bike (bicycle)

#1
Does anyone have a cheep bike they would either kick down or sell. I would prefer to not use the subte, or the colectivos, and walking isn't cutting it.

Cheers,
Brandon
 
#2
I would like to know where I can rent a bike to ride along the river around Olivos to San Isidro? Also, what type of sportswear is decent to wear on the train. If I wore shorts, would it be tacky?