Ok I'm in menards at the galv plumbing pipe. 10ft long, 2 in is 40, 1.25 is 23. Pricy stuff. I can't find any brackets here that I could use at all. Gonna look for fence posts next. Maybe I'd be better with wood.
Don't use the $40.00 dollar ones. You don't need to. The 1.25" at $23.00 is all you need. You only need four posts at the most for an 8 or 10 foot pier unless you want to add a couple more. If your longer posts on the end are plenty long enough you can get away with using only two posts and cut off two shorter pieces to drive in at the shore line.
I'll be happy to find you four of the sleeves up here from a local Menards if you want the next time I go to Angola, IN. I think they are under $10.00 each but don't remember the exact price.
I'd stay way from wood for the support posts. Harder to install in an existing pond too.
Another possibility is to make your pier on land and install wheels on the from two posts. You can get them from Menards too. Adjust your pier above the highest water line you expect. Then wheel it in.
Either way this is a two person job.