Your options are to take the course or to accept a fixed penalty of £100 and three points. And that's the very best offer you will get.
If you go to court it will cost you a minimum of £159. The guideline fine (for a guilty plea) is a third of a week's net income. The court uses a minimum assumed income of £120pw for those with little or no income. You will also pay £34 as a "Victim Surcharge" and £85 costs (in some areas that figure is £90). The only advantage to taking the matter to court is that you can ask to pay in instalments but the court will not accept less than £5 per week.
Courses are being held online at present and there are a number of providers, some of whom charge less than others. You could have a look at another provider, but I doubt you'll see the cost much lower than £100.