How do I build a cheap fence around small garden?

You could use wood stakes and bamboo mats. Or you can use steel stakes with wire fence. Both are relatively inexpensive. If you want a gate that will involve a little more skill and expense.

chicken wire, and posts. the posts need sunk into the ground- a mallet works well for that. your posts can be any thing that will hold up the fence- metal piping, broom handles, pickets from a retired fence...

You could see if you could get salvaged Tfence post, they are fairly easy to put in. OR posts meant for electric fence. Depends on HOW much you want to spend AND WHAT you are trying to keep out! Is it for decorative primarily? Or keeping kids out, or dogs? Bunnies and deer?

Thanks for ideas