The deals thread in the forums is usually very quick to post deals. There’s also a list there of reputable HA dealers. Always shop around as prices vary a lot.
If you haven’t already, you might also want to take a look at the following:
If your main concern is really reliability, though, SmartThings may not be the best match for you. It is a very powerful, versatile system, but it requires a lot of handholding maintenance and typically there’s some flaky bug introduced every two or three weeks. 
It won’t affect all customers all the time, but it’s just a reality of the system.
The company is very aware of this and has made improving reliability their top priority, but they just aren’t there yet. The zigbee update last week is a perfect example. It improved things for many customers, but for some customers it broke things which had been working well for months.
If you need a highly reliable system in this price range, I would suggest Lutron light switches combined with Eve motion sensors and Apple’s HomeKit. You can also add the Phillips hue smart bulb system if you want. All of these devices also work with echo so you can use both together. This is a very limited feature set compared to what you can get with SmartThings, but it meets the high reliability requirement.
Different things work for different people. Just be honest with yourself about what kind of reliability you require, because in general the more features and flexibility a low price system has, the lower its ongoing reliability will be.