Let me point out a misconception about PID's that you just noted. This is common, and it comes up all the time.
A PID is a control device, and not the actual "switch" that control the load (the heating element). The PID sends a low voltage DC, and very low amperage control signal to one side of a SSR (solid state relay). The PID does not actually power the SSR, it only provides a control signal. DC signal present = SSR closes the other side of the circuit which performs the same function as a switch (but it's not a mechanical switch, it's a logic device). So there is no need to "oversize" the PID. What you would want to properly size is the SSR. Most PID builds use a very common 25 amp SSR. This uses the low voltage DC control signal to control or "switch" up to a 25 amp 110 to 220v AC load on the other side of the SSR.
Although the workings of a SSR are not exactly like a mechanical switch, the easiest way to visualize what a SSR does is to think of the load side of the SSR as a momentary light switch and the DC control signal as your finger flipping the switch. Finger on switch and the light is on, finger off the switch and it flips back to off.
Since the element in your ECB is working and performing as desired on cooks, I would stick with it and just add the PID controller unless you have some need to oversize or increase the wattage of the element (go much higher and you will be into a 220v element and will need a special outlet on your deck to use it).
As to programability, the Auber units have it and so will a PID that you buy for a home made build (most of them will). Just double check the specs of the unit you are looking at. On the Auber pre-made, you do not have to use all of the functions and can just use it as a simple "set and control the pit temp" unit if you want (single probe), or a "set and control the pit temp while monitoring the meat temp" unit if it's a dual prob model.
As to buy pre-made from Auber or buy quality parts and build? If you buy quality parts from Auber you will be close to the cost of the pre-made units. Yes you can source parts from eBay and other online auction sites. They will be coming from China and may or may not be the actual brand advertised. If you get the real deal, it may be OK, but if you get a knock off clone (which will look exactly like the real deal because counterfeiting is common in China), you may get a dead or not fully functioning unit. Factor in the possibility of having to repurchase the parts a 2nd or even 3rd time (or give up on China clone junk and spend the money on the Auber for the 2nd go round), I would just go Auber. Good customer service, and they actually back their warranty. I've exchanged private messages with more than member here who got dead or partially working parts from an eBay seller that were clone knock offs. Buying something for half price is not a savings if you have to buy it more than once.
The other thing is the case on the pre-made Auber. Not every one has the tooling to machine the openings so cleanly for all the components like the pre-made Auber. Like I said earlier, it's built like a tank and is all metal. If you make your own, you need to think about the cost of the PID, the SSR, the case, the jacks in the case, the heat sink for the SSR, the safety fusing, temp probes, etc.... and the price starts to add up.
And the final consideration is you will be working with household AC voltage and amperage that can kill. If you have any doubts about the circuitry and how the entire unit is wired, buy the pre-,made or work with a friend who has the necessary skills to build a home made unit safely. Wire a PID or SSR wrong and you will at the very least blow the unit. At the worst you get a very nasty shock that could possibly be fatal. Pre-made avoids this. If you have a friend who is an electrician or heating & ac technician (or any professional who works with electrical control circuits), trade them some BBQ for their help.
Not trying to talk you out of a home made unit, just use quality parts, and be 200% sure of the safety of your build.
Oh, and if you do build your own, make sure you use the schematic that is actually printed on the side of the PID and SSR when you design the wiring layout. SSR's are usually all the same as there are only 4 connection points (2 for control signal in, 2 for switched load or the heater), but the number associated with those terminals can vary. And polarity will matter on the DC side of the SSR for the control signal. PID's will vary widely so a drawing of one someone else made that you find here may or may not match the unit you buy. Even if it's the same brand and model number, they sometimes change the pin out (what connection number is for what function) on the PID's. The drawing on the actual PID will be the correct one.
Let us know what you decide and we will to walk you through a build, but it's best to have someone actually there who knows about AC circuits and AC safety. Sorry I'm so wordy, but I want you to make an informed decision (and be safe).