Before you spend money on customs, you owe it to yourself to try a decent pair of universal in-ear monitors with some good isolating foam tips. If you do decide to go custom, there are several companies that can set you up for under $400. As you've seen, there are plenty of companies who charge much more if you have disposable income.
These things are amazing. I have the Sennheiser EW300 and the buds that come with it (retailing ~$100) aren't really anything special on their own, but with the Comply tips....it's really quite good considering it's a single-driver bud. I'm about to throw down on some A4's but I'm not hurting right now, I can hear everything I need to once everything else is blocked out.