Which Neutral Density Filter?

I've been wanting to try long exposure shots (>30sec) during the day, where moving clouds and water become silky smooth. I need a neutral density filter (or a stack of them), but I never bought one.  I've done long exposure at night where it's dark enough that I don't need ND filters, but cannot do it during bright daylight.

I go hiking barely once a year on average. And the number of waterfalls I've seen in my entire lifetime is still less than the fingers in my one hand. So, forget about waterfalls. Seascapes and clouds might be a better fit for me. Still, I'm not so big into nature or landscape photos. So I read up how much investment is involved and what I need for this play. 

Here is my summary:

0.3ND = 1 stop = ND2 (1/2 transmittance)

0.6ND = 2stop = ND4 (1/4 transmittance)

0.9ND = 3stop = ND8 (1/8 transmittance)

Lee big stopper = 10stop  = ND1024 (1/1024 =0.098% transmittance)

Everybody seems to love Lee big stopper. It is always out of stock in US online stores, and usually have 6 months wait once you put an order. I heard Singapore has a lot in stock if you have someone in Singapore. 

I want at least 0.6ND or 0.9ND.  I don't need graduated ND filters. 

Cokin P holders are good, but filters themselves are very bad. Plastic films whereas Lee filters are glass. 

Singh-ray filters are good. They are screwed-in filters, not square plates that need a holder and a thread-converter. 

This Singh-Ray vari-ND filter http://www.singh-ray.com/varind.html goes from  2stop - 8stop. But $340!!!  (for 77mm thread.)  I can't splurge $340 for something I will try just once or twice. 

Hitech ND filters are good as well, and lower price than Singh-ray. 

With ~$100 budget,  get hard 2-stop or 3-stop. 

http://www.amazon.com/Complete-Neutral-Density-Filter-Compatible/dp/B00867PFZY/ref=cm_cr_pr_product_top

By stacking 3-stop+1-stop filters, I can make 4-stop.  Is it enough for blurring water and clouds? Do I need the big stopper?

Scott Kelby tutorial on 9 stop ND filter. 

http://scottkelby.com/2011/my-tutorial-on-shooting-long-exposure-black-white-images/

DIY: If you already have a circular polarizer, then you can add a linear polarizer on the top of it to make a variable ND filter. 

http://digital-photography-school.com/create-your-own-variable-neutral-density-filter

I have a 58mm circular polarizer, but no linear polarizer. Forget about it if I have to buy another 58mm linear polarizer to diy. 

update: DIY using a welding glass for 10 stops (tip from Jeff )

Still undecided what to buy... I just want to try it once or twice.