Envelope Fonts (for Save the Dates)

Finally getting a chance to mail merge my list into word and creating my mailing labels for our save the dates.
Just realized that when I choose to have my return address printed on the envelopes, I picked a font that isn't on my computer.
Am I crazy to want to try and get the font online to address my labels? Or should I choose something totally different?

What is the font? Is it really expensive and worth the cost? Is the return address printed on the front or back of the envelope?

You probably don't have to get the same font especially if you only want to use it once, unless its really unique and you love it, maybe get the same font you actually used on the save the date?

I like mixing fonts up if they look nice together.