I googled 'buy backpack in Bali' and got this:
can we buy backpacks at the markets or cheaply somewhere? - Bali Forum - TripAdvisor
"1. Re: can we buy backpacks at the markets or cheaply somewhere?
Jun 12, 2012, 10:31 PM
Yep a fair few places stock the cheap ones.
Poppies Lane 2 is where I bought my last one."
"3. Re: can we buy backpacks at the markets or cheaply somewhere?
Jun 12, 2012, 11:14 PM
The
department stores always have a great range of backpacks in all shapes, sizes and prices. I have bought a few over the years and have always found it better to shop in Bali."
Go to Discovery and ask in the stores there
"5. Re: can we buy backpacks at the markets or cheaply somewhere?
Jun 12, 2012, 11:40 PM
try
super nova shoping center its the place the locals shop 2x large bag shops at the main door the cheapest you will find in bali we got a great back pack to use on the scoter cast $9.00 aus and it is so strong has pockets both sides"
supernova shopping centre (I think) is located somewhere on Jalan Raya-Kuta (ask at your accomm for the location)
Supernova Shopping Centre Reviews - Kuta, Bali Attractions - TripAdvisor
Kuta Beach Shopping - Where to Shop and What to Buy in Kuta Beach
Good luck
If you cant find it, you might have to take a TAKSI
Plenty of taksi drivers are nice and speak english and run the meter
I doubt it would cost more than Rp20.000 each way
60 litres is a big backpack