Perhaps the economics are not so ridiculous. IF you know nothing about cars so DIY isn't an option. Consider a brand new Kia Rio 1.4cdti, run for 7yrs and 90k (12k pa). This is a pertinent example as it's what my colleague has just bought £13,500 plus £500 for 5 services (5yrs worth).
Assuming 2 remaining services are £150 each.
Car cost: £13,500
Finance cost £800 (based on double what I've just paid for £15k bank loan over 2yrs)
Servicing £800
Tax £210 (£30 pa)
Insurance £1260 (based on actual quote for me of £180 pa)
Fuel £10,600 (based on his actual 50mpg)
Residual £1500 (guess)
Total cost: £25,670
Vs an omega
Car cost: £800 (buy a good'un, treat yourself

)
Servicing £500 (£70 pa - probably would need more than this)
Tax £2100 (£300 pa)
Insurance £2100 (based on actual quote for me of £300 pa)
Fuel £19000 (based on my actual 26.5mpg)
Residual £200 (scrap)
Total cost: £24,700
So, for the privilege of lying under your car for 7years, you've saved a grand total of £970. Or £2.66 per week.
Now, it's arguable that an omega is a nicer place to be than a Rio. However, that's personal opinion so should not be considered. Especially as some would argue being easier to park and more reliable is more important! I've also not factored anything outside of routine servicing, again I think the Rio would benefit if this were included.
Now, you could lpg, and assuming a 40% fuel saving you would save a further £6k (after fitting cost). However that adds a further level of servicing. Also it's not practical for everyone and would still only see you make savings of £20.87 per week.
If you aren't someone who can DIY, I'd wager the miggy would cost you significantly more. Perhaps let's not be so quick to rubbish the new option

.