There aren't any third party lenses of which I am aware. Certainly not new for less than $150 USD. The closest thing you'll probably find is the Canon EF-S 24mm f/2.8 STM pancake. Of course being an EF-S lens, it only casts an image circle large enough for an APS-C sized sensor. If you are using a Canon M-series camera, the EF-M 22mm f/2 STM is relatively inexpensive.

In general lenses made specifically for APS-C cameras will be more budget oriented than lenses made for full frame sized cameras. Sigma's "DC" series, Tamron's "Di II" series, and Tokina's "DX" series of lenses are for APS-C sized sensors and can be considered equivalent to EF-S lenses. Unfortunately, most of their APS-C lenses wider than 35mm are zooms, not primes. The EF-S 24mm f/2.8 STM mentioned above along with the EF-S 60mm f/2.8 Macro are Canon's only two EF-S prime lenses at any focal length.

The problem with wide angle lenses in the EF mount is that they must use a retrofocus design to allow focal lengths shorter than the distance between the front of the lens and the focal plane. Both EF and EF-S lenses have the same registration distance, also referred to as the flange focal distance, of 44 mm in front of the image plane. A retrofocus lens is like a telephoto lens in reverse. The wider you get, the more complex, larger, and expensive such a lens becomes.

If you don't need autofocus Samyang/ Rokinon/ Bower/ Walimex/ Falcon/ Albinar/ Opteka/ Quantaray/ Bell & Howell/ whatever else they're calling it this week make some fairly affordable wide angle prime lenses. They're all made in the Samyang factory in South Korea and marketed/distributed by a variety of nameplates. Among the various resellers, Rokinon seems to have the best warranty service setup in the U.S. The 14mm f/2.8 ($339) and 16mm f/2 ($360) lenses are APS-C only. The 24mm f/1.4 is also FF compatible at about $460.

Sigma once made a relatively cheap 24mm f/1.8 DG lens but it has been discontinued for a while. You can find used copies for around $250-400 in the U.S. A few places still list new copies at around $550 and up. The replacement 24mm f/1.4 DG Art lens is bit pricier at around $850.

Older, used copies of discontinued versions of Canon lenses such as the EF 20mm f/2.8, EF 24mm f/2.8, EF 28mm f/1.8, and EF 28mm f/2.8 can sometimes be found on a budget. Canon still lists them for between $400-500 at their direct refurb store, but it's hard to find them actually in stock as they go quickly when they are listed.

Any wider than that and the "budget" market is dominated by zoom lenses made for APS-C cameras. But none of them are anywhere near "pancake" sized.

To get a full frame sized image circle wider than 20mm gets expensive fairly fast. The Tokina 17-35mm f/4 Pro FX, Tokina AT-X 16-28mm f/2.8 Pro FX, or EF 17-40mm f/4 are probably the cheapest options for that.