If you read the details of this SlickDeals post, it has all the information you need. But basically, you have 2 options. Go to Walmart around 10 am - 5 pm when you’ll more than likely catch a cellular rep (not a regular Walmart person) and ask for the Straight Talk $49 Deal which you can get if you buy the $149 iPhone SE 3 on Straight Talk and activate it right there and then with their Silver Unlimited service plan which costs $45, with Auto-Renewal OFF. After the phone is activated, you can then purchase the SE 3 and take it home with you. Use the phone in their service (do some calls and texts) for 30 days. You only need that 1 month active service for it to auto-unlock in 60 days.
Second way of getting it is through Straight Talk’s website, that is if you can snipe one when they do get some in stock which is always random. The Notify Me option doesn’t really do jack. You’ll just have to keep on refreshing the website and hope you stumble upon an available one and snipe it as fast as you can. Anyway, once you get one, add their Silver Unlimited plan that costs $45 (with Auto-Renewal OFF), then it automatically deducts $100 for you, which makes it so you essentially just spent $49 + $45 = 95 + some dollar-ish tax for a brand new SE 3 which can become a full fledged unlocked iPhone SE 3 after 60 days.
It’s $99 on the website so is it on Walmart only in person.