As mentioned, why not buy a 125, run it for a month or so and sell it on. Plenty of demand for them so it wont hang around for long.
With a bit of planning you can get something decent for less than a grand, run if for a while and then sell it on for just under a grand. Ok, its a bit of hassle and you need the money up front, but will be cheaper than renting (though not as good as borrowing).
Insurance and stuff isnt expensive either - I did this and managed to get a CG125 for just over a grand, insured for £60 and a tank of petrol lasted ages! Sold it for just under a grand 2 months later.
I needed to tax it just before selling it - I did think that 6 months would be fine, but the DVLA dont allow it - though £16 for the year didnt seem too bad after all...
;D
