You can also consider buying when it's on a level of sale that fits your budget, but keep an eye on the two hour timer for no-questions-asked returns, and if at an hour and 45 minutes, you don't think it should be interesting, consider doing a refund. I'm not sure that you can really get into the game properly in two hours though, at least in the sense that you won't get a thorough understanding of the breadth of the game and won't see much at all of the depth.
I'd recommend reading AARs as the most effective way to get a feel for the game. I don't consider video to be a great medium for Dominions, although although YouTube has them most plentifully. There are a handful of good Dominions 4 AARs that I could recommend, but since Desura doesn't exist any more, I can't find the links to any but
my own. Still, some should turn up in Google.
Edit: took so long on this that I got triple ninjaed.
I'm a short term Dominions player, I've been playing for 4 or 5 years now. It's just that the small map selection turned me off, and I was wondering if I should keep playing 4 and wait for a price drop.
The small map selection isnt as big an issue as it might seem. All the old maps still work fine, there's just some new graphical features that they don't have. And there's now Steam workshop support for maps so it should become easier over time to find lots of good maps.