The invitations I designed from scratch turned out amazing!! I couldn't find anything I really liked in a template so I designed by own using Adobe Illustrator. I think it's definitely a do-able DIY if you have software/skills to do it! I'll share my invites with all of you - I had to blur some information out since my FH doesn't want uninvited guests showing up/some privacy surrounding our wedding, but you get the idea:
Invites with envelopes
Invitation
Details card
RSVP card
P.S. the fonts used were Alex Brush and Adobe Caslon Pro (it came with Adobe I think - the software is on my work computer, I designed the invites on my off-time)