I GUARANTEE you, that as they add features or "upgrades" you can expect $75 - $100/ month for Creative Cloud.
Guarantee? That's pretty bold. But ok, it is reasonable to expect that prices go up over time but if that's your assumption then the cost of one-time version upgrades would also go up. At the end of the day the financial comparison is what you're paying now versus what you'll be under the new model.
If you're a PS only user your upgrade cost every two years was $300 (do I have that right or was it $200?) so your average monthly cost was $12.50 (more if an upgrade came out after 18 months). Now you're paying $20 per month for PS... which is more and not insignificant but you're getting constant upgrades with new features instead of Adobe having to hold them back for a full new release, some cloud storage, and the right to install on two computers. So there is extra value. Whether those extras are worth an extra $7.50 per month to any particular user is hard to say.
EDIT... and there are reports they are planning to reduce the single app price to $10 per month.