Bike buying advice - new or used?

[Plin]

I'm planning to buy a road bike to get in shape. Shimano 105 or better.
I don't care about the weight nor do I need a lot of expensive
components. Basically, a decent, reliable bike that I'll keep for a
long time.

It looks like Shimano 105 bikes start at around $800 new. I'm wondering
if I'd be better off buying a used bike and either to save some money
or, to get a better bike for the same amount of money (for example dura
ace, etc.).

Supergo has a Scattante 105 bike for $850, which seems like a pretty
good deal, even though I'm not crazy about the name. Is this a good
brand to go with (it's their house brand)?

Also, it seems that most bikes nowadays are aluminum. Personally, I
think I'd rather have a steel frame for better shock absorption, since
light weight isn't a top priority. Does anyone still make steel framed
bikes in this range?

Thanks for any advice!