Mark your calendar for: October 1st (regular submission deadline) and October 15th (Poetry Contest deadline).
What it costs to submit: They have an interesting sliding scale. For a traditional 'the cost of postage' submission via submittable it is $3. For $5 you get your submission but also receive a back issue. I really like this option for writers who have never seen a magazine and are only going off things like acknowledgement pages in collections and pieces found online and attributed to the journal. Then they also have the $10 option which is a submission and a copy of the most recent issue which is great for writers who haven't seen the magazine in awhile or just happened to miss the latest issue.
What to submit: Three poems (up to 60 lines each) or two prose pieces (up to 5,000 words).
What they want: Luckily, they've posted a guide for poetry and for fiction just a couple weeks ago to help you get a feel for what would be right to send. Two quotes they thought were important for poetry with which I agree: from Mary Ruefle "a poem must rival a physical experience…” and T.S. Eliot “genuine poetry can communicate before it is understood.”
Read their full guidelines before submitting (it'd be a shame to accidentally include any personal information and disqualify yourself from their blind judging because you didn't check the full guidelines before clicking away), but you should definitely consider submitting, Lumina is a fine journal.