This appears to be a bug when the $ sign is the beginning of your radio button choice.

One way to workaround this issue is to download the process XML and modify it directly. I found that even when using the $, creating a field rule and setting the condition as the radio button, the first option would be selected even though none of the others appeared in the drop down. If you create all of your field rules using the first dollar amount, save and download the process, then search the XML and update the appropriate values. You can then upload and overwrite the process using the correct dollar amounts.

If you aren't comfortable updating the XML directly, as a hacky workaround, I found that when I added a new field rule and set the condition to the radio button field, it successfully chose the first dollar amount, but the drop down wasn't working to show the rest. I got my field rules set up by making the field rule for the first dollar amount first, saving the field rule, then going back to the radio button and putting a new value at the top. I then let each dollar amount take a turn at the top of the radio button list until I had them all set up, then put them back in the original order. Not a great solution, but one that might work if you only have a few choices. 

Also, putting any character in front of the $ made it work just fine. 

We will look into fixing the issue in an upcoming release.