If the need is to accurately cut decking and floorboards a chop saw or mitre saw (slightly more expensive but will cut angles better) is best. Width of cut is key measure - the wider the better generally. This will be no good for sheet material.
For cutting sheet material (eg: 8x4) you need either a circular saw or plunge saw. A plunge saw uses a track to guide it and will make a clean very straight cuts.
Circular saw is either guided by hand or by running it against a straight edge clamped to the board. A laser will not make the cut any straighter if cutting by hand - this almost inevitably leaves a slightly wavy edge. The need for accuracy depends on what you are making!
Saw blades with light DiY use will last years (5 - 10) unless you hit a nail or similar which can destroy it with immediate effect.
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Circular Saw 
Circular Saw 