Drive-side spokes are a little harder to replace since the sprocket/cassette/freewheel needs to be removed beforehand. It depends how mechanically inclined you are whether you want to dive into the world of wheelbuilding (not hard, just takes a steady hand and a craftsman's mindset). But, even if you replace the broken ones, the others are stressed and could give out at any time. What I'd do:

1) If the hub and rim are of decent quality and not worn out, I'd buy a set of new spokes and re-lace the wheel. Requires wheelbuilding skillz and some special tools to remove the freewheel/cassette/sprocket.

or

2) If the rim is worn out and the hub is marginal quality (crunchy bearing races, that sort of thing), then I'd buy a new wheel. Still requires the tools to remove the cassette/sprocket/freewheel. If it were me, I'd rebuild the new wheel since more often than not they come out of the factory without stress relieving and tension equalization.

Somewhere in between, I may clip out a good old rim or hub and re-use in a new wheel build, or save for the future and buy a new wheel. Depends how I feel that day.