I have a USIA suit, and they offer the best prices I can find on custom suits.
The reason, as I understand it, is that they don't make suits until an order comes in. It doesn't take a whole lot of extra work for them to change the sizes, so they don't charge an arm and a leg. I think they charged me around $50 to make my suit longer than one of the sizes on their chart (which has a lot of sizes already). One downside to this is that most dealers don't stock suits and it can take some legwork to look at one in person if the brand is not popular in your part of the country.
I have a techniflex suit. I think the construction is excellent and fabric is a nice compromise for the diving I do. There are times when I have TLS-350 envy because of the light thin fabric, and there are times where I'm not worried about the suit rubbing on the boat or a wreck and the other guys are searching for pinhole leaks. Every type of drysuit fabric has it's pluses and minuses.
Their undergarments are also a great option for affordable custom sizes.
The only knocks I can give them is that (a) their dealer network is pretty weak in some parts of the country and (b) sometimes they get backed up with large orders (usually government orders?).
I've had good customer service experiences both from the factory by phone and in the USIA forum here on SB.