Pets are the income. You dig up eggs, place them on the plot, and the animals they hatch earn cash over time. The official description also says that cash keeps coming while you are offline. The HUD prints that directly: Cash Earns Offline.
Place an egg and read the timer
Select PLOT on the top bar. Eggs already set down show countdown text. One frame listed a Godly egg at 17m 16s, a Transcendent egg at 0m, and a Zero egg at 8m 46s. A 0m timer means that egg was ready to resolve. The frame does not show which animal comes out, or a rarity rate.
The same words — Godly, Transcendent, Zero — are also shovel names. An egg countdown is not a shovel offer. Check whether you are looking at the plot or at the SHOP board.
Selling is separate. SELL on the top bar is for loot you dug up. Pet cash arrives on its own. Both are spent on shovels and on the plot upgrade when a cash price is shown.
One upgrade offer that was actually on screen
An opening plot frame shows Upgrade Plot with the line "5 pets", a cash price of $600K, and a second cost marked with an egg icon. That is a single visible offer for a plot that is expanding around five pets. It is not a formula for every plot level, and the egg-icon amount was not readable. Read the board in your own server before you pay.
The official text says to expand the plot to make room for more pets. More pets are how the offline cash grows. There is no published income per pet, so do not plan a shovel purchase from a guessed rate. If you want a payback guess, put your own extra cash per cycle into the calculator and use a real shovel price as the cost.
Shop tracks that are not shovels
On the shovel shop screen, Hatch Luck and Animal Income both showed as Unclaimed. A Rebirth control is on that screen too. No cost or reward for those three was readable. Do not treat them as free, and do not copy a shovel price onto them.
Index is a button beside Shop. Its rewards are not shown in the frames used here. Open it in game if you want the collection list; this page will not invent index payouts.