As others have suggested, it's very difficult to make money renting out a nice plane.
It's awfully tempting to think "most of the stuff on rental is such crap, there must be demand for something decent" but THERE ISN'T. Well, not if it costs more than a penny extra. This is
UK GA, the land of flat broke pilots who are mostly struggling to make 12 hours every 2 years.
And anybody with 2p to rub together has already escaped the self fly hire scene (by buying into a group or - for IFR pilots - by buying outright) and is absolutely not looking back.
I know, I've tried it myself.
It can be made to work, however:
You start with a piece of wreckage, spend the absolute minimum on it, and run it into the ground. Of course you will probably not want to be flying it yourself after all that, but hey you did want a business didn't you?
There are other issues with rental.
A lot of people rent out a plane because they want to fly it themselves and renting it out reduces their operating costs. HMRC attack this as "not a real business" and they go after the owner in various ways. If owned by a limited company they hit the Director for Benefit in Kind. The well publicised BIK defence (the Director pays the same rate as the renters when he flies it himself) doesn't work in this case. PM me if you need more info...
By the time you get reasonably fussy about who flies it, there is almost nobody left. I used to rent out a very nice new IFR tourer, and this is a quick sample of the enquiries/customers I got:
1 promised 50hrs/year and delivered 2
1 (instructor) promised 130hrs/year (IR training) and delivered 2.5, and fiddled with the fuel flowmeter to reduce his billing
1 promised 30hrs/year and delivered 10, then lost his job
1 (airline pilot) promised 30hrs/year, then his wife had a baby
1 had an expired IMC Rating and wanted to fly around France with a compass and a stopwatch
1 (instructor) "had an IR" but got lost in France and had to scud run all the way back at 1000ft, his IR turned out to be long expired
1 (instructor) with a bogus ATPL, kept inventing various in-flight system failures to get me to chuck it in and put the plane on his school fleet.
1 nice chap but flew his last plane into a hill in fog (amazingly he survived) after a DIY IAP
and so on. I also got assorted hassles like people popping over to Le Touquet and doing their own fuel duty drawback claim and pocketing the money from it, which paid for their whole trip. The next person could not do a claim of course. I had to write some rules after that, allowing drawbacks to be fairly shared out.
It's very tempting to think that airline pilots (the obvious well funded, current and competent customers) will be queuing up to do flights in a nice IFR tourer, but actually they are usually sick of IFR. Most of them either hate flying full stop, or they want to fly rag and tube types to grass strips.
As I say, it can be made to work, in the right situation and with a hard nose. I know of one apparently successful business renting out some DA40s and DA42s, nice looking modern planes, but they are doing it on a busy GA airport where there is no competition. Wel there is the usual rental junk but it's not sufficiently cheaper.
If by any chance you do want to fly yourself and are looking for a way to spread the costs of operating something nice, put together a group of like minded pilots.
And don't bank on avtur being duty free for long. It is likely to go up to avgas levels, except for AOC holders. The DA42 will still be cheaper to fly than say an SR20 but the margin will be small on the grand scale of direct operating costs.