Ryan Seacrest will sign a rich deal to host the new version of "American Idol," but it's not nearly as rich as the one Katy Perry signed.

Our ABC sources tell TMZ ... the deal is expected to be signed this weekend. The sources say the network offered $10 mil, Seacrest wanted $15 mil and they compromised somewhere in between ... but closer to $10M than $15M.

TMZ broke the story ... Katy Perry snagged $25 million to appear as a judge on the show.  

We're told the network, along Fremantle and Core Media --  the show's producers -- have not picked the other 2 judges, but whoever it is they'll be relatively cheap ... because they have to be.