I bought my 1971 Sprint Veloce back in 2002. When I bought it it was in a box, in pieces. It cost around $2,500 plus an extra few hundred for a new strip and paint job. It was relatively reliable for a while but the 30-year-old engine started giving me trouble about a year later. I replaced the engine and it was a lot better after that.
That said, older Vespas and Lamborghinis are finickity.
If you are looking for reliability buy a new(er) scooter. If you aren't looking for the styling of a new style Vespa, I'd recommend a Vino. I know a few riders that have them and love them. I don't know what the pricing is like. You should also check out
The Genuine Scooter Company. They sell new and used scooters, but also sell their own brand: Stella. It's based on a PX Vespa and is, from what I've read, a good choice.
I don't think you are going to get a new one for less than 3K though.