600TB would come out to around $50000 which for Twitter is peanuts. This is their bandwidth pricing though but I guess they'd use snowmobile export (if that exists?) instead.
For reference, 300PB (the amount referenced in the article) using the same pricing would cost $25M. Still might be a reasonable one-time cost for migration for a large corporation, though, even disregarding the "bulk" rates they'd see at that scale.
AWS Snowmobile cost is $0.005/GB per month which comes out to $1.5M/month for 300PB for however long the data is on the truck.