Hi,
The only way this might work is if the drivers had a
radar detector. Then you would have to hope they don't catch on to the fact that there are no police officers nearby and then start driving erratically again.
Something that would help would be a radar trailer such as the
Decatur Onsite 350, but this is more in the budget of a municipality than an individual.
Handheld radar guns range from rather expensive to very inexpensive. A good inexpensive model would be the
Bushnell Speedster II radar gun. This would never hold up in court, but you can use it and sit at the curb all day recording your findings. Take this into your local police department and they might find it worthy of having a partrol car monitor your neighborhood.