If your on a tight budget, try eBay.... might be second hand but you can get some pretty good deals there.
bear in mind you will probably have to pay a garage to lower you sax unless you can do it yourself, cos of the torsion bar needing lowering...
id say invest in some 60mm VTR lowering springs, they fit Furios and westcoasts..thats what ive got my wescoast lowered on. i think thats the lowest u can go without loosing handling, personally i think anything other than 50/60mm doesnt look good enough.
thats just my opinion though
good luck with the lowering mate