Tulle netting(bridal netting)is very inexpensive, usually comes in 72" widths and different sized mesh. It can be found at any fabric/craft store and at Walmarts with fabric departments. Wind, sun and rain go right through it and it will keep bugs and some animals away from your plants. I used it on my zukes a few years back to keep deer from munching on them. I only had to secure it to the lower leaves with clothespins but you'd have to secure it around your container to keep the butterflies out. HTH

Oh, and you might have to hand-pollinate while using it unless you choose the larger mesh that would keep the butterflies out but let in smaller pollinators.
Sorry, I haven't used the floating row cover cloth so can't comment on that.

Don't use the frost protection row covers as you might cook your plants. You want to get the lightweight row cover material designed for insect protection, not insulation. You will need to remove it for part of the day to allow for pollination once the plants start flowering. Like the above poster says, tulle would be a good choice.

Thanks for the good suggestions. I used the larger tulle one summer to keep the Japanese beetles from the blooms on my roses. Appreciate any comments. Always, two heads are better than one. Barb