Usually the plan behind plantings at the edge
of ponds like these are too keep other fertilized
runoff water out of the ponds. The fertilized runoff
will cause an algae bloom and oxygen problems
in the pond and cause a real mess.

There are all miniaturized versions of traditional
pond plants - mini cattails and mini horsetail rush
come to mind. In my pond they tend to be slow
growers and, because of their size, they don't
march out too far into deeper water like cattails
can.

otoh, you sited cost, and they can be more expensive
than some pond plants as they won't spread as
fast.

Lizard's tail isn't a very tall plant and likes to grow
and spread. It will even head out into moist lawn
but we just mow it over.

What you really want to keep in mind is how much
depth a plant can take. Depending on how deep your
ponds are a plant can fill in the entire pond given time.

Also if you buy any plants from a nursery clean them
all off of any tiny floating plants (duckweed and azolla)
or you'll be back here saying - 'help, the entire surface
of the pond is covered with this tiny floating plant!'

hth!
k :-)