Are you sure?
Because in my country the Orbweaver is more than double... the price difference is x2 +$30.00 pretty much.
Orbweaver is $150.00
Nostromo is $60.00 (sometimes even less)
So my first impression is whoever is trying to sell you their orbweaver, is either scamming you or selling you a broken one.
Razer are known to have overpriced gear on release and many gamers wait till the price has dropped before purchasing.
As for which to get well that depends greatly on you as a person.
The Orbweaver has customization so you can really get the most out of wrist and palm comfort.
The Nostromo is blue, the Orbweaver is green (Nostromo's blue looks cooler but the Orbweaver's material palm grip is more comfortable as opposed to the plastic on the Nostromo)
The Orbweaver has more buttons (this can either be an advantage or disadvantage).
For most people it's an argument between price.
IF you can indeed get an Orbweaver for $90.00 then it's probably a good deal and you should take advantage of that, however do you really need the extra's it has over the Nostromo?
Those are questions you will have to ask yourself and I just gave you some insight on these very similar, but very different hardware pieces.
I was in the same boat last year, in the end I decided on the Orbweaver, earlier this year when i was about to purchase it I decided it's overpriced and didn't. I am not regretting not getting it. (As I still plan to, but not until the price drops considerably) Close to what the Nostromo is going for right now. (So it needs to drop from $150 to $60 which will take a few years
)
In the end I am sure whatever you decide will be a good choice, the good thing here is you can't go wrong either way. IF you decide to not take either of them, Logitech has a similar one and a few years ago Z board also released something similar but the Nostromo and the G13 really dominated. Where as the Orbweaver just ensured Razer took the crown.