As has been mentioned before, it's the same as a one-speed vespa but with a 12v CDI designed to fit in the copy of the vespa points case. Read up in the wiki and do some searching, we have copied and translated all the kit/pipe/stock case tuning etc info from vespa-ciao.nl.
Vespas can be made fast, but are expensive to make fast fast. 45+ will be tough on Your budget, definitely rules out variating it, and probably aftermarket cases and fancy carbs. Good news is the carb and case can be opened up to 13mm, and with the rotary valve intake you can increase duration by cutting the crank. Again, read up on how to do this, it's all well documented. If You wnat to know what I'd suggest:
-65cc malossi (torquey, reliable, easy to port match), I haven't looked too deply in to the new kits in the last few years, may be some better choices around now. That olympia reed-valve looked interesting, and I suppose one could get all crazy and run two carbs.
-Bore carb to 13mm
-Bore intake to 13mm
-Case match to kit
-Cut crank to kit spec
-Proma or Tecno circuit (Pipe fit is similiar to ciaos, not much room for the header between the stand and pedals, so there are few choices without ditching one or the other or cutting and welding).
-Lighten clutch shoes
-Smaller rear pulley
Again, all of this information is well documented, read through the how-to's etc, and let us know what questions You have.
This should have You under budget and flirting with the low 40s, If You are a full sized man like myself You won't be going much faster, steep hills may be a problem, and pedaling off the line will be required to save the clutch. In fact, buy some spare shoes or a ciao clutch for backup.