Looks like a pretty typical greathelm to me, maybe a little wide at the bottom but still pretty typical. It's sure to be a sturdy helm.
A few things to keep in mind about greathelms:
1.) They're HUGE. Make sure that you get measurements off yourself and from the armorer:
- Head circumference at the brow -- Wrap a layer or two of blue camp foam around your head and get the measurement. Compare that to the brow measurement from the helm.
- Length from the top of the upper plate (where it meets the "cap" of the helm) to the bottom of the helm on the side -- Compare that to a similar measure on your own head, from your crown to your shoulder. Really big greathelms will actually rest on your shoulders (as they were probably originally intended to). While that's fine and good for jousting, it will annoy the crap out of (and possibly physically hurt) you when fighting on foot.
2.) They have a flat top which loves to catch weapons and will make a good loud "thunk" when it's hit (will be a dead giveaway to the judges that you were hit solidly.)
If you have more cash than time, by all means buy it. But I'd have to agree with Stephen here and say just build one yourself. A greathelm is too easy to make for you to fork out $100 and then spend your own time and effort modding it. You may as well start from scratch and build it to your own specifications to begin with. You can easily build one in a day by yourself, maybe even half a day with help from someone who knows metalworking.
If you want to test it, go
here and print out the pattern* on some card stock, or print it on paper and trace onto manilla folder or poster board. Then cut out and tape together. That will give you an idea of how simple it is to make and will also allow you to size the pattern up/down and trim here and there to fit you better.
There is no specific Ordo requirement for ocular size, so the default rule of "whatever you're comfortable with as long as it isn't unreasonable," would apply.
And Laygeaux actually has a greathelm.
* Brass cross is purely decoration and 100% optional.