Evo 8 Brembos have a larger piston size so more braking power, but its pretty minimal though. You will have to pay for discs and conversion brackets. Also Evo 5 - 9 brembos are all exactly the same as far as I recall. Here's a walk through guide for it showing you what you need.
http://speed.academy/nissan-240sx-br...liper-upgrade/
For ease of installation, I think R33 Brembos callipers and discs are a direct bolt on for S14s but you will be paying more than £300 unless you get lucky
http://www.ebay.co.uk/itm/Nissan-Sky...UAAOSwA4dWHXQ-
For £300, your best bet might be to get some R33 GTST calipers, a good quality disc and pads and some braided lines all round. Very common swap and all bolt on too, they come up for sale quite often in the For Sale section quite regularly so keep checking back