My advice now is that eventually, you would need something that would mount to your gunnel instead of a transom downrigger bar. I think it opens up the space and is probably neater. I am now thinking of getting some tracks installed and mounted.
But I have done this. Using Scotty removal pedestals and a piece of wood…made my own downrigger bar. All for about USD 120.
As for real boards, I know the Berts and Pursuit and TL all have 8-9 foot transom boards that come with 2 pedestals that need to go on the gunnel. They generally cost from USD299 onwards. I think there was an open item at Gander Mountain somewhere N of Chicago that had a USD100 discount. So I think it was USD199. I might be mistaken. Otherwise, in my opinion, the best deals are probably at Marine general looking at their catalog prices.