My 3,2 Elite has cost £17,951 over 8 years now to buy then maintain to the best levels possible.
Wow. Just wow. I think and I accept I could be wrong, but I think you've spent more on your Omega than I have on every car I've owned, including maintenance for the last 25+ years. It's a close call if I could include the insurance I've paid in that time as well.
Credit to you for keeping a car you want running. But when it's put like one lump sum, it seems an awful lot.
EDIT - No I couldn't get the insurance in that as well.
I guess much of that cost us because main dealer prices ?
I bought my 3.2 MV6 for not much money in Sept 2016.
I've taken it from 163k to 230k and spent probably £2k on it including tyres. Mixture of DIY and Back street repaired. Mixture of trade club Vauxhall parts and eBay specials.
It has only let me down.twice. once due to poor maintenance. (Solid discs got fitted on the back and somebtimeblater a piston came out too far and pissed brake Fluid all.over the road) once due to a leaking radiator.
My biggest expense has been fuel. If I had bought any Deisel car, I'd have been less.poor than I the am.now. I reckon £6k could have been saved. But then my previous diesel cost £5k in depreciatelion over 4 years so it's fine.
Yes and no. I purchased the 54k mileage, excellent condition, full service history, late build, for £4,000 from a dealer who specialised in low mileage, top of the range cars. It was worth every penny compared to the high mileage, poor service history Omega's I was seeing when I wanted to upgrade from my then 3.0 Elite Omega. From then on I have given her the best option I can always having genuine parts fitted when either I or my regular main Vx dealer worked on her at trade prices. For tyres I use a very trustworthy (proved to be by me!) regional garage outfit, but for everything else it is Vx who do the work, usually. However when I last required a cam belt change and the fitting of, Vx, front wishbones, I went with a recommendation on the OOF for SOS Garage Services, owned by Serek. His service is so good, with great knowledge of Omega's, excellent work done, for a very reasonable price, and a very friendly customer service, that I will be driving the fair distance for me for him to undertake future large scale works as required. I also had to have a local bodywork specialist , Lloyd, undertake post accident damage work on her in 2017, the cost included in my total expenditure outlay, who rebuilt part of the front end and resprayed all to make it like new.
So, with a combination of me, the main dealer, the tyre outfit and Serek, undertaking I will keep my beast going as long as possible. Llyod I have penciled in to restore (for £1,000 - £1,500) the rear end when any rust around the wheel arches becomes a problem.
All in all this Omega is the one that I want to keep running for as long as possible because she is worth it in every respect. Currently with 80,800 on the clock she is still a good example, and one of the last. As I have said I am quite happy with how much I have spent over the 8 year time period every time I get in her, she starts, and then gives me a great bit of motoring which, once the lock down is out of the way, will again be more extensive!

As others have said though in answer to the OP, you must select the best Omega example you can, with the lowest mileage, the best service history, then be prepared for the regular maintenance costs - there are no cheap, just make do, options on that - with great input when required, beyond your must do DIY, from reliable, proved to be, professional outfits, including taking advice from the OOF experts, and never be afraid of some big bills that keep your Omega in first class running order.
