No problem or any questions I'd be glad to help I'm a trusted listia seller and buyer also if I have your zip code approx weight an dimensions I could calculate or tell you the exact box and shipping price
It's actually up to seller discretion unfortunately but you could tell em hey you know I got two items can't you cut shipping a little and send in one box or come up with a fair price and see if they go for it or you could make arrangements with them to pay one and extend they payment date of the other if money is an issue some people are understanding and will help you out others just want to get the extra cash from shipping so that they make a few extra bucks
Ok looking at USPS that's the cheapest it's so weird 5 day shipping says$10-$13 and for 2 day shipping is $16-$18 that's kind of odd but whatever it looks like the best deal is two day shipping through the USPS
However the program for shipping I have doesn't have anything about flat rate boxes but I'll be right next to a post office tomorrow so I will get the full answer tomorrow