Golite packs are on crazy sales everywhere you look right now. They're solid packs and tend to be quite lightweight.
My wife and I made the transition into ultralight backpacking with Golite Jams, which aren't the lightest packs out there, but are still very light, durable and capable of holding a lot of gear. At roughly 20-22 oz, we still use them today. These packs have been as low as $40 lately. You can also find them lightly used on this forum all the time.
An ultralight tent is going to set you back. Unfortunately, that's just the way it goes. Again, if you buy lightly used from this forum, you'll save some money. Still, you get what you pay for, so you might as well splurge a bit here and get something awesome.
I love my Tarptent. I bought it before we ever even thought of getting trekking poles, so I bought a Cloudburst 2. It's extremely sturdy and comfortable, and it weighs just over two pounds. My wife, dog, and I all fit in it pretty comfortably. It was $275, but worth every penny.
The good news is, you can save a lot of weight without spending much at all. Just leave stuff behind.
For instance, you're interested in a stuff sack system. Why bother? Leave the stuff sacks at home and use a 2 oz trash compactor bag as a bag liner. It's waterproof and white so you'll be able to see the gear inside your bag pretty easily.
One beautiful thing about going ultralight is that you have far less gear, so organization isn't nearly as important. You don't need lots of pockets and stuff sacks to keep things separate. For the smaller items like repair kits and first aid kits, ziploc bags work just fine.
Speaking of Ziploc bags, ever think about freezer bag cooking? How's hot food in under ten minutes with zero dishes sound to you? Awesome? That's how it sounded to us.
This lets you leave behind everything but a small pot and a couple sporks. With no need to simmer food, you can build a $3 penny alcohol stove that'll boil enough water for dinner in just a few minutes. Best of all? My entire cook kit (stove, pot, windscreen, lighter, spork, and mesh bag to hold it all together) weighs 5 oz. When I made this switch, it saved me about two pounds.
Really, going ultralight is just getting used to a different mindset.