Fraid it is that bad Ninja, the leon is not a track day special its one of the super copa cars, or the earlier TOCA versions. BMW M3's make incredible race cars. A well driven clio cup will mince a huge array of vehicles obviously being true renault sport cars, and the suzuki is pretty much a single seater with a cuppachino body.
You'll def be allowed in, eligability is never an issue in the eurosaloons (I raced it for 3 years, and Trev Nyssa7 for even longer), but there's plenty of experinced racers and ealthy chaps in it. You will need huge power or a very good base car, in other words a fiat coupe (bravo?) wont cut it, you could buy a much better car for a lot less then it takes get the fiat any where near competitive.
If you like driving on a track do track days, but dont get to attached to you car, because if you want to go into competition then plan that move with a car which will beat the rest, for example in hillclimbs the sub 1400cc road class could be the best way to win the championship with a well planned purchase, points are awarded for class wins you might not be the fasters car in the day but if you are the fastest in your class you'll get the same points as those is the 'higher' classes finishing the same place.
Just a note on circuit racing
You need an ARDS test (cant remember the cost)
Once you pass you pay extra for the license
Then you have to join the BRSCC (for example)
Then you have to join the race series eg eurosaloons
You need race suit and lid
Then you have pay to enter a race
All that cost before actually getting on track,
In sprints
Apply for clubman B license
You join local motorclub (cheap)
You enter sprint
Lid
So much cheaper then circuit racing.
Have a think, look at all tin top, saloon car series. Consider the costs, look at whos leading the classes (look them up on youtube also), then plan you entry. Send me a PM and I'll send you my number if you wish.
(trev in my car at Anglesey)