Welcome to the community!
Firstly, you should note that Fido no longer offers a purely pay-as-you-go pre-paid plan. All of their current offerings require either a pre-paid monthly or yearly plan. As such, the minimum charges would be dependent on the plan chosen. It should also be noted that the text messaging allotment with the Yearly plan is applicable for both incoming and outgoing SMS (see here).
In addition, you should also note that -- likely due to the recent US shutdown of their '3G' networks -- US roaming is not available with pre-paid plans (see here). You can view whether roaming is available at your destionation as well as the pay-per-use rates here. Roaming charges only apply if you make or receive calls (including checking voicemail) and sending SMS. You wouldn't get charged for incoming SMS. However, since data is not available with pre-paid plans, you would unlikely be able to receive any data within MMS.
Hope this helps 😀