Allow me to add to Alan's reply. As a former realtor, you need to know that "technically" realtors can show you any home for sale BUT...if the seller has a listing contract with a brokerage, there is a clause / understanding that the seller ONLY wants financially qualified buyers to view their home. This means any realtor you want to work with will ask you for either a pre approval letter from a lender or proof of funds. Realtors do reserve the right to REFUSE to show you any homes until you provide a pre approval letter or proof of funds.
If you think about it this way, yes there are buyers who would LOVE to see a multi million dollar mansion except they can't afford it. This explains why realtors will only show you homes that you are financially qualified for. There is also a realtor's concern for safety. A pre approval means a lender verified your employment, income, credit, savings, debt, etc. and that lender has your social security number + contact information. If you had other intentions, it would be easy to track you down. Without a pre approval, why would a realtor risk their safety if you are not a serious buyer?
Regarding For Sale By Owner listings, a realtor can show you these homes also BUT...the issue of paying your realtor needs to be discussed and in writing before showing you a For Sale By Owner listing. You can view these homes on your own also.
If you want to see homes that are outside of your budget, you can always go to Open Houses that are typically held on weekends.