I really think that the credit shop prices should be brought down.. diamonds are still 150

They won't be. There have been several threads about this topic in the past week. They will be kept there. Once people run out of diamonds, prices will re-stabilize so you needn't worry. These 30 mtc diamonds are only so people can get mtc so they can buy spawners, which in turn grant them an unlimited money supply.

My only complaint is with the cost of lava, same creds as a diamond for a single lava block just isn't worth it when I can fill an inventory of 36 buckets with lava in a minute if I just go to the nether.

Think of it this way. Lava buckets are not stackable, but lava blocks are. As well, you reduce the cost of hard currency (iron to make buckets). You also save a bunch of time from having to walk down to lava level / going to the nether to get lava, and bringing it to your site. I actually think it is priced right for all in consideration.

At the exchange rate of 1d=3g=27i=9 buckets, 3 iron is hardly a cost... perhaps if buckets weren't reusable I'd see your point.

Look at it this way, if I used /home a huge lava pool in the nether and the build site was near a warp, I could collect and place 36 lava in a few minutes. But I couldn't find and mine 36 diamonds in the same amount of time.

I'd think that a gold, 50c, would be a sufficient cost to be worth spending the credits on, without it being obscenely cheap.

Again, lava buckets are NOT stackable. That, in itself, is a lot of cost.

Also, two days votes gives you 21 lava blocks.

Considering the voting, that is why the cost is there.