You do not need a subscription to register your node on the network. Subscriptions are only necessary for creators using rndr.otoy.com.
Please checkout our community made calculator for an earnings estimate: https://www.rendercalculator.com/
Render work is not assigned through a bidding process, but based around Tier allocation, reputation score and availability.
Reputation score is based off a "proof-of-render" system, whereby human job confirmation and algorithmic rendering checks are used to confirm work. This disincentives "bad actors" from rejecting correctly rendered work, and pushes less work towards low performing nodes.
For node-operators, a slice of work rendered is taken and assessed for success in order to calculate a reputation. This is weighed against the node's rendering history, which prevents swings in success to negatively affect a historically good node.
We plan to expose more information on how reputation score is calculated through the API and a user dashboard that is in production