I'm looking for an inexpensive (under $30) custom shades online. Everything I find is REALLY expensive, and I was just wondering if there are any cheaper retailers out there. Thanks!

What type of shades are you looking for? "Room darkening" doesn't really help me help you. Black out shades are the only type that truly make a room dark and they are very expensive. On the otherhand there are inexpensive blinds available but it depends what you are looking for. If you want a type of blind that will help darken a room then you have to go with aluminum or wood rather than vinyl.

For 35$ a roller blind would work to darken the room.

a vinyl blackout shade for $35

So I guess what I'm seeing is a lot of shades for a 36" window that cost about $35. What size are your windows?

If you are looking for the absolute least expensive solution then go with ikea.com

See here

None of the curtains or shades at IKEA are available over the internet so hopefully you have a store near you. You could also check a place like Sears or Target/Walmart for cheap solutions.

Vinyl Blinds are generally referred to as either "Room Darkening" or "Light Filtering." The room darkening ones don't actually make the room completely dark, they're just thicker than the light filtering blinds. I don't need the rooms to be completely dark, I'm just looking for some cheap custom sized vinyl blinds that will filter out a good part of light.

Many home improvement stores (Home Depot, Lowes, etc...) sell blinds. They cut them to fit right in the store or if you buy them online then you trim them yourself. (pretty easy) While they aren't the best quality, they will filter out the light. Off brand blinds are a suitable fix until you can buy something of higher quality.
Blinds at Home Depot online

This link doesn't seem to take you to the right page. In the search at the top just type in the word 'blinds'. Click under 50.00 and you will see the options there. There are many prices.

Less than $10 (37)
$10 - 20 (67)
$20 - 30 (57)
$30 - 40 (19)
$40 - 50 (18)

I purchased some blackout blinds from 247 Blinds.

Blackout blinds

(Make sure you measure the window correctly as I had to have them fixed)

Measuring guide

Hope this helps