A 5 Litre (1.3 US gal) pot is the biggest pan I have at present. I would like to make some all grain batches. How much beer can I brew with such a small pan?
If your pan is 5L, you will only be able to make less than that, depending on how much of your wort evaporates during the boil.
Perhaps 3,5 to 4L, unless you do multiple boils.
I would go and get a bigger pan or look at starting with extract brewing.
In a 1.3 gal pot you probably shouldn't boil more than 2-3 liters because you want to leave some head space to avoid boilovers, which can be a huge mess. With boil-off, you're going to end up with even less beer than 2-3 liters, unless you top off with more water. So it's probably not worth it to brew in less than a 2-3 gallon pot, so you can safely brew 1 gallon batches.
Brewing is a hobby that costs money - the ingredients cost money and the equipment costs money. It doesn't need to be expensive - you can buy economy pots - aluminum or thin economy stainless - and brew great beer. Brewing less than 1 gallon at a time (~10 12 oz bottles) probably isn't worth the effort. You can also get yourself an inexpensive 1 gallon glass jug for fermenting.
Brooklyn Brewshop is a small company that only sells 1 gallon all grain kits. They have a good videos that shows their basic process, which utilizes a strainer for sparging. You could also do brew-in-a-bag (BIAB) with a small strainer bag, like those used for partial mash brewing.