From your example, my understanding is that you are looking for a match of:
col1 starts with 0-9 or col1 starts with A-Z. Is that understanding correct?
If so, I would suggest using a "Extract with regular expression" step and selecting "Create a special found column" with the regular expression:
Here's an example of the step:
This will provide you with an output column with the values true/false, where the true values meet the condition: starts with A-Z or starts with 0-9. You can then filter on your found column to filter for "true" matches.
To answer your original question regarding a formula step, you can use the < and > operators within a formula to represent "in between". So if I was looking for the column 'col1' and wanted all values in between 0000 and 9999 for example, you could have a formula step that is: col1 > 0000 && col1 <= 10000. For the use case you outlined here, it seems like a regular expression would be the easiest way to evaluate though.
Let me know if you have any questions about this approach.