I just got an email through from Final Draft with a discount code.
I already have it but if you enter DM413 during checkout BEFORE Wednesday 10th April then you'll get $100 off bringing the price down to $149.99.
I know it's still a lot but if you're seriously into script writing then this is the industry standard and any directors you work with will expect scripts through in .fdr or .fdx formats if you're collaborating.
It won't improve your writing skills but it will make it look pretty and enable you to do a load of stuff that other software won't.
If you don't have the money but do want some script writing software then I would highly advise Celtx as a free alternative.