Reasonable question. I have previously published some information on having a spare HERE, but for those that want a quick answer....
Most Motorhomes already have receiver for hitch so adding a spare carrier there should be relatively easy. Amazon has some and I have seen smaller models starting at $40.
One way to cut cost is to put one of your old tires under a cover as a spare.
Used wheel from junk yard should also cut the cost.
Re: Tire cover. I would consider a WHITE cover a necessity unless you want to bake the life out of the spare mounted outside the RV.
RE jack & tools. Be sure you know what you are doing and have all the tools you might need including flat board & steel plate if you need to jack on soft ground. If you don't already have the tools I suggest Harbor Freight, as hopefully you will never need the tools and if you do they will not get much use.
Will you be able to physically lift the tire and mount it on the RV? You will need correct 6 point socket and a 2' breaker bar and if you have a Motorhome with dual tires in the rear an extension. You should practice at home so you know how much effort is needed.
Here is a YouTube one guy made. Your system may be different so after watching, you can go and do a practice on your RV.
Even if you can't do the physical job having a spare will probably pay for itself as any road service should be able to change the mounted tire so you are not confronted with having to buy a mismatched new tire @ 2x the normal sale price.