don't forget the cost of the EBS volume. that'd be an extra $5/mo for 50GB of storage

Yes, you're correct. But its the same $5 no matter what instance size you use, which is what this spreadsheet is for.

Also, on my small slicehost, I'm paying $20/mo for 1/3 the RAM, and using 6GB of disk, which would be $0.60 on EBS.

Well, you don't need the EBS volume on other instance sizes, because they have instance storage.

Nothing durable, though.

That's a lot cheaper than an extra 50GB on Linode.