Wow that's cheap for shipping by the time you have added the foam esky, breather bag and packing they must be shipping them for free. Maybe you could provide us details of this seller tva. I think half of the street price from a brick and mortar shop is realistic for Gumtree sales. Neos in Adelaide aquarium shops seem to be around; cherries $3, bloody mary $10, red/orange Rili $10, blue dreams $14, blue/black/brown diamonds $6-10, yellow $6-10, culls $3-4 or cheaper for bulk purchase, so half of that. Most sellers on Gummy are offloading juvies or their culls that are pretty small where as you can selectively hand pick what you want from the aquarium shop and that are much larger adults of breeding age or not far off. On gummy you are pretty much getting a random scoop of the ones they don't want, so factoring that in they need to be cheap for people to want to buy them. If the shops don't have stock you might get away with a higher price but there are goods stocks around in Adelaide at the moment especially for neos. I think you would be kidding yourself if you expect to get shop prices for shrimp that people hand cannot hand select themselves. Never had the greatest luck with Gummy solid juvies anyway once you factor in the mortality rate getting them up to breeding adults you would have been better off paying a bit extra.
I think you are better off getting a API Master Test Kit & API GH+KH test kit if you can afford them as as it is more accurate and work out cheaper in the long run. If you are happy with a round about the Tetra strips are probably the better ones. Steer clear of the API test strips as they really suck. Really only comes down to time if you are happy with a round about that takes less than a minute go with the test strips or go for the liquid if you want a little more accuracy but takes you 10 times longer to get the results. TDS pens are worth their weight in gold, great for acclimation new shrimp to your tank as when you get matching TDS/Temp results you know its time to pop your newbies in. also gives you an indication on when to change your water.