thats not a simple question (especially for me with my poor english)
i will tell you what i did and what it cost me
bigger i/c, for 156 thp we use the seat sport for ibiza i/c
https://www.google.com/search?q=ths+int ... VojhjQs10M:
this one is what i have and it cost me around 400 euro with the installation
bigger exhaust from downpipe till back cost 850 euro
mini cooper jcw hybrid turbo, bought second hand for 600 euro (sold mine for 300) paid 60 euro for installation
ideally you should buy also the jcw manifold (don't have it)
ecu reprogramme cost around 300 euro
this setup will produce more than 250 hp but cant prommise anyone that he will reach 270
for higher numbers you will also need new pistons etc.