Looking at the pet search, the cheapest is currently priced at 120,000 tu.
You can check the value of creatu by clicking "Search Pets" on the sidebar. Here are the settings I usually use:
Location: Rancher Shops
Species: whatever species you're looking for
Color: whatever color you're looking for
skip
skip
skip until you get to price
Price: 1 to ___(leave second space blank)___
On the other side, don't change anything except
Set Order By: Price
Then hit "Search" :)