A $30K license is only a problem if you're giving your services away for free. With a quad or 6-core processor (remember MS charges per socket not per core) you can power about 500-750 spindles. You're looking at $200-250K to build a single socket system that can be fully utilized. (eg. 128-256GB of RAM, 3 or 4 controllers, and 500-750 disks) The problem is that people stupidly put SQL EE on a commodity box with 8 GB of ram and 2 spindles and then complain that the software is 5 times as expensive as the box.
Also, $30K is the retail price for the license, no one actually pays that, and if you can write a little bit of code you can easily use a SQL Std license for $2-5K.
As much as I dislike Microsoft, you have a point. When compared to serious RDBMS hardware costs, 30K is not much. And you won't go much further on an SQL database than SQL Server or Oracle can take you.
If you plan to go further than that, you should have an exit NoSQL strategy ready.
Just as a sidenote, when making the plan, keep tabs on the downtime needed to migrate your data and on ways to migrate users to the new system in batches. When you get too big for SQL you are also probably too big for big-bang migrations.
