on the subject of ur selling ur backpack for cash:
only real way is to convert the whole thing into keys, then sell those on marketplace.tf
best way to convert to keys is to find someone whos buying whole backpacks through backpack.tf , but people who do that generally want significant discounts. unfortunately, theres not really a way around this unless you wanna try to sell everything individually.
tldr: sell australiums and unusuals to quickbuyers, sell everything else to someone buying backpacks, then sell the keys on marketplace.tf
ur prolly looking at 80-100 dollars cash in the end, depending on the type of items u have