How to shop for wines

[acaines]

My wife and I like to have a bottle of wine every once in a while. Neither of us are experienced, but we know what we like. We tend to like wines which are on the sweet side, but not too sweet. Berringer makes a white Merlot which we really like, but there are other wines available and since variety is the spice of life, we want to expand our palette. The problem is we don't buy wine all that often. Therefore, we don't want to ruin a nice evening together by buying a wine we don't like. I do look at price... anything that sells for less than $5 for 750ml I avoid. Usual price range is $6-$15/bottle, but definitely open to higher range for something really special. Would also like to venture into wines from other countries like Chile, Australia, Germany, Italy…
Any suggestions?

Some wines we have tried:
White Merlot-- Our current favorite.
Chardonnay-- A bit acidic for our tastes.
White Zinfandel-- Nice, but we like white Merlot better because of its fruitier taste.
Merlot-- Not bad... a bit heavy for our tastes.
Muscat-- Nice dessert wine.
[Soft]Chenin Blanc-- Enjoyable, however a little sweeter than we like.