Luckily, CG can be very budget-friendly. Don't be scared by all the expensive or hard-to-get products people use; sometimes they're great but it's definitely possible to build a basic routine with what's available and relatively cheap.
About growing your hair out long, this board won't bring you as much help as the "Growing Out" board, there's a ton of info over there you can and ought to sift through (I am too, growing it out).
Co-washing: This is probably easily everyone's cheapest step. All it takes is some cheap cheap CHEAP conditioner like Suave Naturals, Whiterain, or V05. I personally prefer Suave because it's a little thicker, but others love the other options. Best, they're cheap enough to try them all, if you want (all run about $1), and you can even pick these up at places like dollar stores and Odd Lots for even cheaper.
Rinse-out: Depending on the state of your hair, you may be able to use Suave or the others as your rinse-out. Many people can't do this, but it won't hurt to try. Suave Coconut is probably the most moisturizing of those 3 brands. Otherwise, you'll have to hunt a little for a cheap, silicone-free conditioner. There's many options at places like Whole Foods, but there's also a big, usable conditioner at Trader Joe's that runs about $3.20 or so (I don't use it, but lots like it for co-washing or sometimes rinsing out). It's called Trader Joe's NourishSpa. There's also a dark green bottle by Garnier Fructis (Triple Nutrition I think) that is cone-free. I'm sure others can add more options.
Leave-in: This doesn't have to be something different from your co-wash or rinse-out unless you feel those are either too light (co-wash) or heavy (rinse-out). I use Suave for this, too (can you tell I'm also on a budget?), but I need to "seal" it with coconut oil (there's much info about this, but here's the gist in my case: this prevents moisture from leaving my hair, if I apply a tiny bit of oil after the Suave. Instead of buying a better more moisturizing conditioner, where there's enough moisture to leave and still have enough in my hair, I just seal the little bit of moisture Suave has. This keeps costs way down, as a huge jar of coco oil was about $8 and I use it everyday and probably won't need another one for at least a year. Still, this isn't an option for everyone and I'll probably need a heavier conditioner for winter if this doesn't keep working.). Otherwise, there's a slightly pricier leave-in available at Target and WalMart and Whole Foods for about $8 called Giovanni Direct Leave-in. This is very popular and is a good beginner product.
Stylers: There are ENDLESS options here. There's Boots (if you can get someone to send this to you while they're in England, it's very cheap, but otherwise shipping is very costly), and here in the States we have L'Oreal Out of Bed Texturizing Creme, which is getting slightly harder to find but I've seen at Walgreens. There's Kinky-Curly Curling Custard
, which is expensive at $30 for a large large tub, but many people claim the number of uses they get makes it a worthy purchase (personally I hated it and swapped it after using roughly half). It's a VERY popular item and is available at Whole Foods (used to be online only, so consider yourself saving even more). As for gels: Herbal Essences Set Me Up (gel and spray gel), Body Envy, and Totally Twisted are all options. Set Me Up is probably the most popular of the 3 HE gels. Garnier Fructis has a couple (remember to check ingredients), as well as Suave and L'Oreal. Just remember to check the ingredients of anything that looks interesting. Those gels typically run about $3-4.
Benefits of second day hair: For a tight budget, obviously the fact that you don't have to use your products again is a huge benefit. Most people find they need to refresh second day hair (even if they use a satin cap or pillowcase, which prevents frizz formation). You can try this with water, water and gel, water and a curl cream, or a product alone, or a spray bottle with water and product mixed, conditioner...lots of things work (and are cheap!) and you'll just have to experiment.
Other items: I like using honey as a styler, and I am definitely not alone. I mix a tiny tiny dab of it with my leave-in, and it gives me hold (I don't need a lot, but it does provide some) and shine and adds definition.
Many people like vinegar rinses, which are cheap, but I cannot stand the smell so I never do it.
Beauty supply stores: I forgot this! Sally's, Ulta, or Trade Secret all sell salon products or knock-offs or other non-drugstore items. Sally's is best-known for its knock-off of Biolage Conditioning Balm, which is about $6 for a nice tube (and for most it's so moisturizing the cost is not an issue/ you can also get this knock-off at Walgreens for a bigger tub for about $14 and it's called Bioinfusion Conditioning Balm). Sally's also has Lustrasilk cholesterols, which are about 3 or 4 dollars for a BIG tub, but be sure to check the ingredients, they are not all CG (mineral oil is not CG). The safe ones are Olive Oil (very popular, green tub) and Shea Butter Mango (also popular, orangey-peach color). Those work really well as rinse-outs and leave-ins.
Whew! Enjoy my novella.