When did you actually receive this notice and have you responded to it?
The post is a bit confusing because it only previews the jpg image of the NIP. Above it is a hyperlink to the pdf scan for the COFP. So it would appear that initial notice was responded to and the OP is now in receipt of a NIP.
OP as suggested, the time factors involved probably prevented the offer of a course being made. I assume it is a works vehicle that is leased to your employers, so you were possibly third in the chain.
It is unlikely to get better than £100 and 3 points if you take this to court. You don't appear to offer any defence to the allegation, more that £100 is a bit steep. In court you would have costs and 'victim surcharge' added to whatever fine amount you received, which is 50% of weekly salary discounted by a third for an early guilty plea. The only advantage you could seek is time to pay.
Generally speaking, a speed awareness course usually costs around £100 so other than the addition of three points, there isn't a cheaper option outside what you have been offered.
Edit to add: Assuming you do accept the COFP in the end, don't ignore section two which needs to be completed with your licence details and sent off to the ticket office, regardless of whether you have paid the fine online or not.
We have a lot of people come here who have ended up with a SJPN because this wasn't completed as instructed.
The licence number you previously submitted while identifying the driver is not taken into account. They need it on the returned COFP as well.
