FWIW I'm getting the 'real-time NYSE data' (not the level two data but real time level one) for $2 / month on my tradingview membership. Not exactly breaking the bank
The speed and format of the data is the other, and major component of what you pay for.
You are paying for what we'd call display only quotes, meaning you get these quotes so a human can visualize where the market is. If your strategies are based on trading once a day then this is fine for you.
The other way in which you will be throttled is how many quotes you can view at once.
If you trade options you won't be happy with only being able to view, say, 20 SPY contracts at a time as there are 1000's of contracts for sale.
Ideally you'd be able to view 20 contracts per date( once a week) multiplied by 2 for both puts and calls over the next 3 months, which is 20 * 2(put and call) * 12 (3 months of 4 week contracts).
This is alot of data to stream over the internet considering that those quotes probably change 200 time a second each.