If you want a skimmer, it's better to just save until you can get one that performs well. It's not a necessity at all, especially when the tank is new. I would look at the Tunze he mentioned and see if it'll fit (I knew there was a Tunze that fit these), then just save until you can get it. With skimmers a lot of the time you get what you pay for, except for a few exceptions that are overpriced garbage.
And while we're on new tanks, you may want a small 10 gallon to quarantine the fish in before you put them in the tank. Most fish come with diseases and parasites these days. And trust me, you don't want any of that in your main tank. There's an article on how to simply setup a quarantine tank on here.
Also, you should wait at least 3 weeks - a month between adding each fish. The biological system has to adjust. If it's overloaded at once you'll have problems.
I'm sure you know this isn't a cheap hobby to get into. But for the most part, once you have the equipment, you're set. So buying a $26 skimmer, when you can get by until you can afford a better one is a waste of money.
A lot of people buy the equipment in steps. It's just the necessary stuff you need in the beginning (like a tank, stand, heater, filter, filter media, thermometer, rock, sand, net, food, and a tap water dechlorinator like Seachem Prime if not using RO/DI water).
I have been piecing together a 180 gallon tank for about 6 months now. I already have a 93 gallon cube and now have to rebuy all of the same equipment in a bigger size. I can't afford everything all at once either.
But if your new to saltwater setups, make sure to read how the nitrogen cycle works and a simple quarantine tank.