I completely understand the cost factor. I too jumped in without the ability to purchase everything up front and the desire to sort of take things slow.
So, a couple of things from that angle.
1.) Second hand can be your best friend. I say this from a couple of perspectives. First off, if you can find a local club you will likely find someone who is downgrading or taking out or upgrading a tank and can likely find live rock for much cheaper than I have seen online and at lfs. In addition live rock that comes from an established tank is an excellent source for beneficial bacteria. (oops, just saw you don't know anyone with a tank....but ask at the lfs there may be a local club)
2.) I can't tell where you are located from your profile, but if you are in the states, I've got a gentleman that I just purchased my skimmer from at a very reasonable price, and when the used one I purchased was broke in shipping, he was great about getting it taken care of and sent me a new one for the difference in price. GREAT guy to work with, I'll PM you his info.
3.) On the skimmer. Since you've read through the forums I'm sure you've seen several brands of skimmers mentioned. They range in price all the way up to several hundred. I know others have differing opinions, but what I have read, and heard from some of the local guys is the following. One of the things you want to look for is that it has a needle wheel pump. The venturi pumps work, but general consensus is the needle wheel pumps are better. Second, especially if you're going to keep corals, you can't go by the rated gallons for the skimmer. Every company rates their skimmers based upon a their own definition of appropriate bio-load. On some brands they will tell you rated for "X" gallons at low bio-load or "X" gallons for high bio-load but that it really only a guideline and is only a few brands. I've seen it recommended many times to go bigger than your gallonage. There are 3 reasons for this. One, it's better to be over skimming than under skimming. I think that in general we tend to overstock our tanks, so having a higher rated skimmer is beneficial. In addition, corals like good clean water, you want to get as much out as you can. Second, you're likely gonna upgrade your tank someday. You are then faced with upgrading your skimmer. If you buy a large enough skimmer, you may be able to continue to use it with a bigger tank. The third point I've seen is that if your skimmer is big enough(i.e. you bought enough skimmer for future upgrades), you could potentially only run your skimmer intermittently, thus saving wear and tear on the pump. Ultimately the pump is the only moving part and will likely be the first to wear out. All that being said, brand is largely a personal preference based primarily from personal experience. From what I read, it's sort of a "you get what you pay for" in that the higher quality tends to be more expensive. The two brands that are more economical that I've read about is the Eshopps and AquaC Remora Pro. I'm not endorsing either of these products, just echoing the reviews etc. that I have read. Personally I just purchased the HOB Eshopps skimmer (PSK 100H) primarily because it got good reviews and was within my price range. That's a LOT more skimmer than you would need even in the 20 gallon. They do make a 75 gallon version but even that may be more than you need. Hopefully someone else will read through this and offer an opinion/experience as well.
4.) Back to the second hand, and expansion on the local club. I understand that not all clubs are the same, but just for your reference, I plugged into my local club and have several guys that are more than willing to frag their coral pieces. The best part of this is that they are willing to sell them to me at a fraction of the cost of the lfs. I don't have a good selection of lfs in my town, so this is really a blessing. I bet you will find some folks in the hobby that are more than willing to do frags, etc. and will be reasonably priced, if not local, maybe at least not far from you. All that to say, you don't have to spend $100 on a frag unless you just really have to have one that is all grown out. Part of the fun for me is buying small and watching/helping them grow.
5.) You can also purchase fish and corals online. Ask around these forums at reputable dealers, etc. as many people buy stuff from online vendors. I know a couple that I have looked into, and the local club guys have shown me a few others. -Nemo- has a couple ebay sellers that she buys from and has received beautiful pieces. I'd much rather support the lfs if I can, but in my case the selection and pricing just isn't feasible. The nice thing about the lfs is if you make friends with them and want something specific, most places can get it in for you and you can avoid the overnight shipping costs. Guess the bottom line is there are Pros and Cons to each. Personally if quality is good and price is about the same, I advocate for supporting the lfs. I won't buy much if any of my fish/corals from lfs because of the quality(and sad, sad state of their tanks/livestock), but I do purchase dry goods and equipment there when I can.
Guess that's enough ramble for now so I'll close. Hope it's been helpful and you didn't fall asleep reading it.
Yuma
p.s. One other resource that I didn't mention is Craiglist. I bought half of my live rock from there from a guy tearing down a tank in a neighboring town. Was a couple hours drive to get it and come back, but it was good stuff at a good price.
/www.fishforums.net/index.php?/forum/73-nano-reefs/
Grayscale - and keep up the good support Yuma 
