Looking for a cheap 20" steel rim for my spare tire

Need help finding a cheap rim for my spare. OEM spare that came with the truck is 18". The truck came equipped with 20" tires/rims. I'm told you can run the 18" spare for a limited time. But I have an almost brand new 20" Michelin Defender (275/60/R20) that I want to use as the spare. Apparently, finding an inexpensive, 20" steel rim compatible with my truck is harder than I thought. I've checked junk yards, Marketplace, auto stores, etc. My online searches only seem to produce expensive rims. I spotted a Dorman 20" steel rim, 5x150 lug pattern, but the vendor site states the rim is not compatible with my truck. I must be missing something.

 

Why does it have to be steel?

 

Doesn't have to be, but I assumed it was the least expensive, and the current spare is on a steel rim. I keep the spare in the truck bed (I have a cap).