I use 4 gallon plastic tubs to spawn my bettas. I cram a ton of live plants in them and a ton of IAL with a lid of some sort for the nest. I only fill them with three to four inches of water. I keep the lid on tightly so the temperature stays stable and the fry can develop their labyrinths. I am now placing my tubs at the top of my 6ft shelf so the heat from the space heaters and other tanks keeps them from 82F to 88F so I no longer need heaters and I can place jugs of clean water up there for water changes.
I like the tubs because it makes moving the fry at 3-4 weeks of age easier. I simply drain to an inch, float, slowly add water, then I pour them into the 30 gallons.
I do recommend a larger tank for your first spawns (10 gallon) but this method has worked best for me.
I get mine for $3 each at King Soopers (Kroger, City Market etc.)