iTunes has season 1 of L&C on sale for $15. The other seasons are a much less reasonable $40.
$40 for a digital copy is kind of insane! I'm pretty sure, when I bought my DVDs a few years ago, that I only paid like $20 or so. It couldn't have been much because I was running on teenager funds. I wouldn't pay $40 for a digital OR DVD copy.
Edit: I just looked on iTunes & for me, all four seasons are $34.99.
In the UK play.com currently has the DVDs quite cheap; season 1 for UKP 7.99 ($12.78) and the other three seasons at UKP 10.99 ($17.58 each), or UKP 20 ($31.99) for two; this offer also applies to a lot of other DVD sets, so you could get Seasons 1-4 and another DVD set for UKP 47.99 ($76.76).
WB Shop The WB store has the dvd sets on sale for $13.75 each right now.