'07 Yaris Clutch replacement

[dinop]

Hi there,
I'm new to the forum and was wondering if any of you could help answer some questions I had. I have a 2007 Toyota Yaris sedan that my parents bought as a daily driver back in September '06. As of last summer it has just become a backup car for extended trips or for the days when my Range Rover 'fails to proceed' (as the manual puts it). The Yaris (as of today) has 272k miles on the odometer and is still running well!

I am having some clutch issues though. Every month it seems like its getting weaker and weaker to the point where I feel like if I tried to drain the transmission fluid the whole clutch would just pour out with it! So obviously something needs to be done. My question for you is:

How much would a new clutch cost if I swapped it out myself? Are there any other options rather than the stock Toyota clutch, for mileage or acceleration purposes? Is there anything I can do about the clutch disengaging when the pedal is at the floor? Is there any way to get it to disengage halfway like in my Audi?