It depends on the party. I love to order pre-printed personalized invites but if it were a casual get together or something, I would just fill in cards. Also depends on if I can find cute cards! I love etsy for ordering invites, they have designers in every price range, theme, ability level, design type...it's awesome.
Fill-in invites definitely don't bother me if it's for something like a baby shower or birthday party. I just do what is easiest, and for C's 1st birthday I just printed cards on our printer. I'd probably think it was odd if I got a fill-in invite for a wedding, though! haha
Re: Is it considered cheap to buy invites and fill them in yourself?
You do what's easiest for you.
For the record, I usually order photo invites, but that's because I like to 1 up the people around us.
I ordered 15 photo invites from walmart.com and spent 9.00