We actually just got Cadbury spayed 10 days ago by AngelDogsFoundation. 20 lbs or less is $110 and Over 20 lbs is $120. Cadbury came home with an e-collar, pain meds, and sedatives (they're not to run or play for 7-10 days). Not only do they get spayed, they also get their nails clipped, rabies shot, and microchipped. All of those are included in the price. As part of the aftercare, they give you a phone number that links you to their on-call doctor...just in case anything happens and/or you have questions. I never had to use it because Cadbury bounced back within the 2nd day. We just removed her e-collar last saturday and her incision has already healed beautifully.

They are a mobile clinic so they are at different locations on different days. I was a little hesitant to go with them since it's like a surgery room on wheels. But trust me, they are so efficient and CLEAN. The staff were soooo nice and kept playing with Cadbury while I was filling out the paperworks....they even got on the floor to cuddle with her. After the surgery, I was worried about how to get my dog into my car. I worried for nothing because they carried her straight to my car and even gave her a kiss on the head goodbye.

AngelDogsFoundation might be a little far from riverside, but it's an option. - http://www.angeldogsfoundation.org/

Pasadena Humane Society has a low cost spay/neuter clinic for the following cities:

Arcadia, Glendale, La Cañada Flintridge, Pasadena, San Marino, Sierra Madre and South Pasadena

They also microchip for only $20.

I assume you live in Riverside, maybe you know someone who lives in one of these cities? Or maybe your humane society has something similar. 

i live in Riverside and it has been awhile now, Maya is almost three.  but she was spayed at Small Animal Hospital on Magnolia across from brockton arcade.  then Mary Roberts Shelter on Van Buren has discount days/events.