Stay with me cause their will be a decent amount of math, but it is GUARANTEED profit if you do exactly what I say.
What you are going to be doing throughout this is buy Spring Break cards for sand dollars at an amount cheaper than what it cost to open the cabana store pack for coins.
Cabana Store coin pack cost 1400 sand dollars for 10k+ coins (for this we will assume you only get 10k however the odds on them are decent to get more and if you get more your profit significantly increases)
10000 coins / 1400 sand dollars = roughly 7.143 coins per sand dollar. Basically buy cards for cheaper than this on auction house (Breakdown Below)
98 ovr is 19000 sand dollars. 19000*7.143 = 135717 coins
97 ovr is 8500 sand dollars. 8500*7.143 = 60715.5 coins
96 ovr is 5000 sand dollars. 5000*7.143 = 35715 coins
95 ovr is 3000 sand dollars. 3000*7.143 = 21429 coins
94 ovr is 1700 sand dollars. 1700*7.143 = 12143.1 coins
93 ovr is 1000 sand dollars. 1000*7.143 = 7143 coins
Personally I bought 98 and 97 overalls for 130k and 60k respectively so far. I do recommend to not stock up on large amounts of sand dollars if you don't need to. The house rules goes away in 12 days and so will the cabana store.
You can only do 5 of these packs each day which is 7000 sand dollars a day. So always check to make sure you aren't buying to much to the point you will have leftovers after the cabana store ends (the conversion ratio after the store leaves will probably be terrible).
Also, if you think playing these house rule games are boring or annoying just come out in field goal block and let the opponent score on you twice to get through a game as quickly as possible to open up the cabana store.
Best time to buy these cards is on promo drop day. Otherwise just check every now and then. Personally I checked like 3 or 4 times, and 2 of the times there was 97 and 98 listed for cheaper than their listed price above.
If you have any questions, just leave a comment and I'll probably get back to you within 24 hours. Best of luck with your coin pack rolls. Hoping for many 20 and 30k pulls.