After making a mage recently I was going through both Street Magic and SR4 to look for ways to take on some flavor spells to round out Charlie's spell book, but at 5 karma a pop it seems like mages are pretty much stuck withtheir initial spell lists and picking up or 2 more over play with the rest of their Karma going to initiation, bonding foci, and raising magic.

Back in SR3 you could limit the spell as you were learning it to make it cheaper instead of to just reduce the drain. Was that considered unbalanced or something? Granted there is more versatility in only needing to learn a spell once, but I think its pretty fair to take some major drawbacks on spells to make them easier to learn. I may not be remembering correctly, but in SR3 were you able to take a Metapalanar quest to learn a spell as well?

It did allow for a certain amount of cheese (such as allowing you to have every spell in the game at Force 2 spells with the Exclusive limitation), but that was because of how those rules interacted with the rules for buying spells (which was based off of Force). They got rid of Force-based spells in SR4, so having those limitations wouldn't have been as big a problem. But as if often the case, people overcompensate and got rid of both options rather than just one or the other.

I still allow it in my game and go a step further, allowing you to have individual geasa on a spell as a limitation or drain reducing option.

Alternatively, talk to you GM regarding Karma awards. Especially if there's a lot of mages or technomancers at the table, there's going to be a strong need for a slightly higher karma spread than in a game without such characters. I know I tailor the karma I give out based on how much people need it in order to advance in interesting ways. I usually give out between 8 and 12 karma for a session which may not even encompass a complete run. Thus, it's possible to end up with around 20 karma for a single episode (which is made up of multiple sessions) which allows for mages to acquire a variety of new spells if they choose to do so.

This does, however, result in powerful characters rather quickly, so your GM should be prepared for that. In my case, my games only last from Sept. to May during the school year as I usually take the summer off from game mastering and try to actually play a game or two. Thus, I don't have to worry about long-term characters at the many hundreds of karma level. It's possible, however, to be at 120+ karma in one of my games over the course of a school year, though, which makes people very happy with their characters at the end.

I haven't looked at it in a while, but in the core book, there is a blurb on fetished spells...just can't remember if those were cheaper to pick up or not.

Limited spells are still there, they where just well hidden (on pp. 172-173 of the BBB).
They don't make it easier to expand your spell list, though.
Goes with the one-size-fits-all approach of SR4 spells.

there was the old cash for karma, or karma for cash rules. cant recall if any book have reintroduced it tho...

Karma for cash hasn't shown up in 4th as far as I know. I don't think limiting spells to make them cheaper is unbalanced in 4th given that the 5 karma cost of spells means that they won't be free after the cost break as opposed to a Mage starting with all spells known at F2.

That was pretty much the only issue Limited Spells had in previous editions, too. At best, using the same modifiers of old, the cheapest you could get a spell is 3 Karma instead of 5 Karma. Not exactly game-breaking.

of DOOM!

I know my GM does this: If you do the research using the Arcana Skill to create your own spell, you do not need to pay the Karma for it. Just need to pay the money needed for the research. Of course, said spell cannot be in the book....

I use TONS of limited spells. Gives a concrete game-mechanicy reason for me to dress like the eccentric shaman that I am. And I get to be creepy every time I remind the game master what the sustaining focus is that I'm using on my favorite spell that might not pass through the word filters here on my work computer.