I saw some adorable flip-flops at Target for $13. 
(Sorry, but there is NO WAY I’ll spend that much on a pair of flip-flops.) 
They were really cute though, and instead of plastic between the toes (I honestly hate ANYTHING between my toes, except sand) they had straps made from satin.

I wanted to make some cheap beach shoes for our Cape San Blas trip

At the dollar store I found some flip-flops for the kids for $1.  (You could use some you already own also, but we had none.)
Also found a pack of bandannas (2 for $1)
and a crazy tie for (yes) $1
You could use any old scraps of fabric you have too.
Grand total on my son’s flip-flops (or chancletas as we say in Panamá.)

I cut the plastic straps out of the bottom of the shoe.  I saved this to use as a measurement for
the straps I made.

I cut strips from the bandanna about 1/2 or so wide.  (You could use any width you wanted but this was for my 5 yr old.)  I took three of the strips and braided them together into a stronger strap. 
Using the Y strap I cut out I constructed a similar one out of the braided straps by taking two braids and knotting them right where the two met.  I wasn’t sure what to do under the shoe, but ended up just knotting it once under and cutting pretty close to the bottom.
It worked!

(Sorry the quality on the picture is so bad.  I took it with my phone, and for some reason my phone won’t upload my pics!  I had to email it to myself to get it off the dumb iphone…)

They lasted, which was what I was worried about, and even in the water on the beach.

I’m going to make my daughter some from the old tie, and will post pics if they are cute!