Tough call honestly between turbo vs s/c for cost vs bang for your buck. But for the avg person non mechanically inclined person, jay is right, s/c is the easiest. However, 300 is a little low. With the right kit, people have gotten approx. 350 whp on the forums with either a turbo or a s/c setup.
However, it is strongly suggested that you at least change the valve springs regardless of which direction you go.
If you pick up a used VF2 kit or BWR REV series kit and the right tune, 350 can be had on a stock motor. There is a guy on the forums, i think his name is Thang35u, who has done a few turbo kits on 2zz's and he has 350whp on his recent turbo build on a lotus. And i want to say you can build a turbo kit for about $3k or less, then you need a tune.
I personally am doing a turbo kit, but mine is about $4k due to engine work and big power. Good luck on your path to "bigger power" through forced induction.
2005 Lotus Elise Graphite Grey - Salvaged title started the SSM build!!!
Maverick ML8 - Other daily
2005 VW Passat Station Wagon TDI (harder to find than the lotus?)
2005 Lotus Elise Starlight Black - Sold