1) Initial pricing of 128 gig Sata III SSDs were right around $200, currently around $100.
2) I bough a 256 gig Samsung 830 and a 256 gig Curcial m4 both for $180 each. Just have to wait for a sale. Although I don't relly recomment the Agility III, But if your laptop only has sata II port it is an option as I think I've seen it on sale for $160 for the 240 gig version. The Agillity III is really a SATA II SSD (performance wise) labled sata III (LOL)
3) based on your current used space a 128 gig would be fine.
Just remember to:
.. manage your swap file, set min and max both to 1024 mbs. Saves about 1 1/2 x ram minus 1 gig.
.. Disable hibernation (saves an amount of disk space equal to Ram)
.. Either disable restore points, or LIMIT the amount of disk space. each restore point takes 300 mbs. 10 restore points equal 3 gigs lost disk space.
PS caution on USB sticks and SD cards - they are NOT all created equal. For SD cards make sure it is a class 10. For USB thumbdrives, check th read/write performance - if not listed, DON'T buy.
Added:
Currently the best 256 gig under $200 is probably the Agility 4 for $150 after $20 MIR
http://www.newegg.com/Product/ProductList.aspx?Submit=ENE&N=100008120%20600038487%204017&IsNodeId=1&name=%24100%20-%20%24200
NOTE: the 240 gig uses the SF controller which I'm not a big fan of.
For 128 gig SSDs
Only one under $100 that I would recommend
http://www.newegg.com/Product/Product.aspx?Item=N82E16820227791
My personal choice is iether the Curcial M4, Plextor M3, or the Samsung 830.
All 3 perform almost Identical in REAL world. However the Curcial M4 or Plextor would be easier on battery.