Firstly is this possible on the stock 1.1 mpi engine. If so how much financial backing will it require?

It is defo possible, a folk back in PL made one with LPG even. There are buts of course, here your biggest concern is the engine management with the Euro-whatever-number two lambda system. Best bet, if you want to have control over things, is to go fully standalone.

But, if it not a micro ECU, there is a way of doing all this on the stock ECU, see here:

https://www.fiatforum.com/cinquecento-seicento/329065-seicento-mpi-turbo-ecu.html

(Would not be myself not mentioning this again )

A lot.

You're probably looking at £3.5 - £4k to do it really well (remember, you also need better brakes, wheels, suspension, tyres).

But cost it up.
Standalone (cheapest is DIY Megasquirt)
Rolling Road time
Turbo
2" exhaust, bigger CAT
Exhaust manifold
Fuel Pump
Injectors x 4
Inlet manifold
Intercooler
Oil Cooler
Turbo
Forged Pistons
Forged Rods

It's probably going to be cheaper to pinch the 1.4 16v turbo engine (T Jet) and box out of a 500 Abarth. More power, better reliability, tougher gearbox.

Oh dear much more than i thaught. I was thinking of low boost on stock internals, i see there is alot involed

It should be possible with decent management (I'd not call Woj's car low boost) and a head spacer to lower compression.

Low boost puts you in a strange place where cars with 1.4 (and even 1.2) 16v engines will be quicker in the real world.

Your insurance will probably be cheaper, but it'll be offset by the fuel costs!

Would an omex 600 ecu be up to the job?

Sure. Omex, Canems, ECU Master, or box of bits megasquirt of the cheaper alternatives.

Boost is addictive (I'm sure my MR2 would be more fun with 300bhp..........) so intercooler and oil cooler would make sense at an early stage.

You need a wallet that needs wheels to move it around and time to boot. If you don't have both buy something with a turbo on it already.