About the only way to save on quality connectors is to close your eyes, bite the bullet, and buy the box of 100 ps. instead of buying a couple at a time. The damn things are simply expensive no matter how you look at it. You may find a local "electrical supply house" carries the same grades for a little less than other sources. The best ones often have a seamless copper tube as an inner lining. That's not tinned, but a dab of silicone grease before you insert the wire accomplishes the same purpose. The seamless inner liner is supposed to provide a more uniform crimp than any type of "seamed" construction. Beyond that...you have to see what is offered and make your own choice about whether it is good enough.
Those blade connectors are not all the same. If you look carefully at a brand name like Fast-On, you'll usually see a dimple neaer the edge of the blade. When you snap their "qd" fittings together, a bump on one piece snaps down into the dimple on the other, making them much harder to pull apart. And preventing them from slipping apart, even with lots of vibration. That's part of the reason why they may be several times the cost of the "500 for $5" packs, they simply aren't all the same.