If you have a dedicated line, that's not for one stream, though. Unless you're streaming 24/7, you won't need that bandwidth all the time. If you were using that bandwidth all the time, you'd be several streamers splitting the cost.
For some more realistic numbers, let's say you get a VPS with 12TB bandwidth. This would last you 5600 stream-hours at 5Mbps. For 25k viewers and two streams a week, you'd need 25*2/5.6 = 8.9 such VPSes.
A VPS with 12TB traffic costs $11/mo at ServerAstra, a VPS with 20 TB traffic costs $3/mo at Hetzner, and CDN networks are even cheaper. Assuming the more expensive one (smaller hosting provider, accepts bitcoin, not hypersensitive to abuse notices), the costs would come to $134/month.
This is outside the reach of a hobbyist streamer, but it's an order of magnitude cheaper than buying a dedicated line, which is the most expensive possible way of doing it unless you intend to be streaming 24/7.