Having been both a hired sales person and an independent sales person, I can say that 30% is normal for a commission only sales person.
Hired sales people at 5-15% commission will also receive a base, which reduces their risk while they get the sales process going. Additionally, it will help them through the sales troughs. They expect a sales process to be presented to them so they can follow it... think of following a rainbow to a pot of gold.
Commission only people take on a lot of risk as they put work in with no guarantee of result. Additionally, it sounds like you do not already have a repeatable sales process in place. You probably haven't done a deal of this magnitude, either, if the value of the deal is only $100k if you do it without the sale person. The first big deal at any level is always more difficult than subsequent deals.
Pay the commission, track the experienced person's sales process, create a killer case study, then use that as a repeatable process for future sales people to follow (at a much lower commission rate). You'll be able to hire a few with the additional $110k in revenue provided by the sales person.
As a side note, I know of Seed Investors that only invest if they can provide Sales/BD services for the first 1-3 deals. They'll take up to 50% commission, but they know that the first few deals set the tone and make subsequent deals easier to close.
More companies fold because of too little revenue vs. too much revenue.