Personally, I'd wait for Guild Wars 2, it looks like a better game than CO and it very nicely allows you to play it all you want once you've purchased it. In essence, it's got a lifetime subscription for only $60. Same thing with Guild Wars 1.
Although, if you really want Champions Online just ask yourself how long it'll take you to play it to your satisfaction. It'll practically be over a few weeks after you get your first character to the level cap. I assume that will take about six months as that's the length it took me to level a character to my satisfaction in WoW and I play MMOs basically in the same way that you do. So, it seems to me that you would save a good deal of money by not getting the lifetime subscription.
If I may make another suggestion, it seems that you would have a lot more fun with a free-to-play MMO. Personally, I find Vindictus to be immensely enjoyable. Especially since it's only money-locked content are cosmetic items so it's wonderfully not a pay-to-win sort of game.
