I'm wondering in general if real-time data feeds can be paid for just one time, then used in various apps like Tradestation, Bookmap, InteractiveBroker, etc. As they are pricey, looking to be as cost-efficient as possible.

Hi! I use the excellent DTN IQFeed.... you're limited by computer, not the number of places you use the feed, I'm fairly certain. I currently run it into Multicharts but can also use DTN's apps at the same time on my PC. It was the same when I used IB data, but note that IB claims to sell you price data, but in reality it doesn't work if you're doing any kind of back testing. I can only recommend TS or IQFeed. J