Is this bike salvageable?
It might be salvageable but the cost of:


new chain ($10)
new tires and tubes ($25)
rear cluster (maybe; $20)
new brake cables and pads ($10)
new derailleur cables ($10)


which is the minimal repair, is going to be around $75 in just parts, that’s if you get the dirt cheapest versions. If any of your bearings or hubs are seized, you’ll need to rebuild them which isn’t expensive in terms of parts (just bearings and grease), but is labor intensive and requires special tools. 

You’ll quickly get to the price of a good used bike if you have to pay labor and even if you do it yourself, you’ll quickly rack up a bill. 

I’d sell the frame to someone who wants to rebuild it and already has all the parts — or find a donor bike with a cracked frame that you can steal all the parts from.