I've lived a lot of places, but I usually couldn't afford to "travel" in the sense of going somewhere and coming back.
Before Covid hit, I had travel plans and had bought a ticket. Now I'm considering a trip next winter, for about 3 months.
I look only at poor/cheap countries, and cheap accommodation (e.g., hostels).
Kayak seems best for cheap airfares, as it provides options from many airlines and travel companies. If I see an affordable airfare, I check the company that is offering that price. Some providers receive low ratings from customers.
I check hostel prices to give me a general idea of what it might cost to stay in a country. I know that walk-in prices are usually cheaper than online rates. However, booking online for the first few nights will give me a chance to recover from my trip and take a look around.
I also look at apartment prices, but anything advertised online tends to be upmarket. Affordable apartments might be found on arrival.
In addition to accommodation, food, and other expenses, airfare and associated costs need to be factored in. So an Asian country might be cheaper than a Latin American country, but the extra cost of getting to Asia cancels out any savings.
Similarly, I abandoned the idea of visiting more than one country. I might get a "good deal" on airfare to a Latin American country, but getting from there to a neighboring country could be expensive.
Sure, I could go by bus or something, but there are problems with that, especially for an older person. For example, you might have to walk across the border, carrying all your luggage. Or, border areas might be considered unsafe.
Some countries require travel health insurance. For me, the cost of insurance would prevent me from going to that country. Some seniors might not be able to buy such insurance anyway (because of age or other factors).
Well, I've rambled on. I hope there was a useful tidbit in there for someone!