I'm looking for an unusually designed one-piece swimsuit. 

First, it needs to have an attached skirt that is knee-length, not
just long enough to reach midthigh.

Second, it must be available in plus sizes, most specifically, size 20. 

A choice of patterns or colors would be nice, but I understand there
aren't going to be many suits out there that meet my specs. I've seen
them before, but not very often.

A link to a sewing pattern would be acceptable, but only if the skirt
is attached to the swimsuit. There are any number of sarongs and
pareos that could create the same effect, but I want a one-piece suit.

The person for whom I am buying this is not at all style-conscious,
but is very cost-conscious. As such, I'm not interested in an $80
imported swimsuit. She would never consider paying more than $40 for a
swimsuit. I might be willing to go up to $50, but any suit that costs
more than that is not an acceptable answer.