I just fitted a Pioneer unit to mine and spent a small fortune on various cables.
Needed one which relocated the hazard and passenger airbag to the lower position (from your pic I don't think you need this) and needed another one to interface with the steering wheel controls. The button relocation harness was cheaper at Dynamic Sounds, but the steering button interface they had was more expensive.
My research suggested that all the various resellers were selling the Connects2 products. Depending on what your setup looks like it will be one of these I think:
Connects2 offer a range of Car Audio Systems, Car Stereos, CD MP3 Head Unit, DAB Radio, Car Radio DAB, AV Multimedia Car CD DVD Stereo, Sony Car Audio Player, iPhone iPod Stereos, DVD Screens, stalk adapters, integrated MP3 adapters , integrated iPod adapters, integrated car audio adapters
connects2.com
Connects2 offer a range of Car Audio Systems, Car Stereos, CD MP3 Head Unit, DAB Radio, Car Radio DAB, AV Multimedia Car CD DVD Stereo, Sony Car Audio Player, iPhone iPod Stereos, DVD Screens, stalk adapters, integrated MP3 adapters , integrated iPod adapters, integrated car audio adapters
connects2.com
Searching by the part number I found some were cheaper directly on websites, others were cheaper on eBay (sometimes from the same retailer)
I got the CTSST001.2AA from Bass Junkies through eBay for £49.99 (price correct April 2023) and had some minor issues with a broken clip - they were great to deal with and it got sorted quickly. Interestingly what they supplied was in a T1 Audio branded bag and the instructions list the part number as T1-ST1v2
I also got the cheapest fascia I could find on eBay and think that was probably a mistake as it's not the greatest fit and was quite fiddly to install. It's good enough and I'm not changing it, but if I was doing it again I'd spend a bit more on that.
As mine was a DAB unit I also got a new antenna.
The kits are convenient, but I saved myself a fair bit of money by identifying the various components and buying them separately.
All works fine and I'm happy with it. Let me know if I can answer any other questions.