Turbo wont give you the boost ratio to cost that you are looking for I assume, your question is vague at best and since you opted for the SE version your intentions where the MPGs. In my opinion your most optimal solution is an upgraded air filter, NGK grade spark plugs with iridium tip and a well optimized ECU. If you dont mind driving deaf a strait pipe would help, but then why a Focus? If you have a bigger budget sell your SE and get an RS all tinkering is done for you..
Search Ford Focus Questions
Ford Focus Experts