I can't see the prices as I have them already, but I bought them not long ago and they were 800 points each I think? Except Leviathan which was 560, but jeez don't quote me on that lol. So no, they don't go down in price which sucks. However my view is that they discount the base game so heavily that it all works out in the end. Seeing how Bioware games are (in my opinion) more replayable than most others I'm okay with saving up and getting everything.
If you get the Digital Deluxe version on sale, as I did, you get Javik from the start, then download the Extended Cut Ending which is free.
You could just stop there first time round. If you know you'll play more than once then you could go naked and just play it as it is now, then buy the DLC another time and go again. I, however, bought the base game on sale and all the DLCs at the same time. It ended up being the price of a regular game, something like £25-£30 UK which I thought was pretty good for a game I'll play at least a few times.
Omega is totally missable, but Citadel DLC is fun and Leviathan teaches you a lot about the ending. Good choices.