Crown Vic, used, P71, low miles. Stop asking.
Al right, yes, but please, no "Dog Units" (K9) or "Vomit Comets" (street patrol units that carrried prisoners, drunks)
because those ones STINK, especially when the temperatures outside get hot, or even warm.
Best of all, are the SAP units ("Street Appearance package") in regular colors other than white, VERY desirable and rare, (priced accordingly) usually
issued to dectectives, Captains, brass, top administrators, and so on.
If you can find them, also White House Protective Unit, FBI and US Marshall cars are good SAP units too..
They are beconing even rarer, now, as Ford hates to paint these anything other than white, to keep costs down.
Another great choice is a one year old rental return, Grand Marquis or Crown Vic, often with just 20k or so, balance of factory warranty, for about $15,000 or so, if you shop around.
Crown Vics are only fleet issue now, so if you want a base Grand Marquis GS, well, you can pick one up for just $18,000 if you shop around carefully.
that is a smoking bargain, as MSRP for these are about $25k to $32K, new asking prices.