Frankly, I would be fine paying $30 and even $40 for expansions IF these expansions contained more of the type of main missions and side missions that started with TTK. But 5 missions and a few side missions for $30 doesn't seem enough unless the raid is Vault of Glass amazing--we'll see come Friday.
And more honestly, these missions don't even seem to be that intricate or complicated, and for the life of me I can't understand why it takes months and months and cost so much (apparently) to come up with 5 of these missions. Must be the ridiculous inefficiency of the engine that has been discussed before, where it apparently takes hours of coding to move a box from one place to the next. I suspect this will be the biggest change to Destiny coming in Destiny 2.