Replace engine/cat/hybrid-bat or the whole thing

I think my beloved 2008 with 185k is on her way out. I was hoping I could pick the hive-mind for some tips for my situation:

I've been burning oil for a while now (I'm talking 20L in the last year), and is suddenly burning upwards of 3L per 1000 miles now... I should also mention during my recent road trip when all this began, so much oil gunked up an exhaust valve, I couldn't get above 40 and the engine sounded like a pressure-cooker releasing steam whenever I gassed it. The dealer cleaned it up for me enough to get power back, but I'm guessing I'll need to replace my catalytic converter and sensors as a result of burning oil for so long... (not sure how much that'll cost). I also figure I'm looking at replacing the engine b/c of worn rings. I don't suppose a piston soak would help...

Prior to this recent development, my replacement hybrid battery from Greentec dropped from 48mpg to 38 in just a few months (my 3rd from them, and last under warranty...), so I'm not sure how much farther that'll get me before she won't run at all either and I have to replace that as well.

So, I'm weighing my options as far as replacing things piecemeal or just trying to sell and buy another used. My main priority is long-term financial economy, and I keep my cars until it's more economical to move on.

I'm waiting to hear back on engine replacement estimates, but I don't know how likely or how much future battery/catalytic (as well as other mechanical) failures are going to cost me. So with that in mind, I just saw a 2008 with 100k miles on craig's list for only $5700.

what do you think? too many upcoming expensive repairs and time to get out?

I'm fairly DIY competent with a moderate amount of auto mechanical experience. If doing the labor myself tips the scales, that's something I'd consider in the equation. Thoughts?