I would recommend Netflix. I don't know where you are, or if Netflix is available everywhere, but if it's an option, I think it's a great deal. I pay $7.99 a month and can stream all the Star Trek I can take - including TOS remastered. I turned off my $80 a month Direct TV almost two years ago now and don't miss it a bit.
I did the same thing a year or so ago. I got Netflix and almost right away shut off my cable. It was a no-brainer for me: I was paying over $100 a month for no HD and hundreds of channels I never watched. Less than $10 month and I was able to watch what I wanted as many times as I wanted. Later I added Hulu Plus so see newer weekly shows. I'm out of luck with sports, but there's still relatives' houses and radio if nothing else. I'll never go back to cable.
As I understand pay-for-stream services like Netflix and Hulu+, and perhaps even what Amazon's doing, you're only buying a one time watch of that episode.
Nope, with Netflix you just pay a monthly fee like you would with cable, it's just a much smaller bill. I can't remember exactly what I'm paying, but I think it's still under $10 a month. I can stream TOS in HD all day long, and all the other Trek's as well. You can also rent the discs themselves, on either DVD or bluray, and they'll send them through the mail, so you can see the things you can't stream like DVD special features or commentary. There are no late fees -- I've kept some movies for nearly a month -- and never any extra charges. As I understand it , the monthly fee is based on how many movies you want to be able to rent through the mail at one time, i.e. you'll pay more if you want to be able to get two or three movies at once instead of just one. I just do the one movie at a time. You keep a list of the movies you want on the main Netflix website, and they send you what's on top of your list. If it's unavailable, they'll instead send you the next movie on your list. When you're done with it you just stick it back in the envelope, seal it up, and send it back out.
The only thing, though, is to be able to stream on your TV, you need a device to stream through. I have two, a bluray player which streams in HD, and a Wii in my room that only streams in standard definition. You can also stream through your computer.
I also have Hulu Plus, which is a flat monthly fee of, I think, $7. I'm only able to stream through my Wii, though. A lot of TV networks are on Hulu, so you get new shows weekly after they first air (and some shows before they actually air). Having Hulu is more like having cable TV, I suppose, whereas Netflix is like going to the video store to rent a movie. I believe both services offer all the Trek series, but I much prefer Netflix to Hulu. I have a lot more trouble with streaming titles on Hulu than on Netflix, which almost never gives me any trouble. It may be that my Wii just doesn't like Hulu; it frequently locks up while streaming and I end up having to do a hard shut down. Really annoying.