You must try to buy when there are less managers conected. For example, from monday to wednesday I bought players cheaper than on weekends. Offseason you see much less users loged, too.
A great time to buy pretty cheap players is when playoffs start. As you won't be able to use 'em, you can nail som free agent or some forced sale (the went bankrupt) and get some cool finds.
The beginning of the season is a good time because a lot of GM organize thier roster, so you'll have plenty of chances.
In the end, is a lot about patiece and several tries. Check the market everyday, iin fact, any time, and eventually you'll nail it.
Now, don't expect an 18 year old MVP fo 1k because that won't happen ever.