The only two agencies in Monmuth County that use digital systems are Atlantic Hghlands PD and Asbury Park PD. The Atlantic Highlands system cannot be monitored by any scanner, and Asbury Park's system is P25 digital, which the newer scanners can receive, but it's full time encryption, so they can't be monitored either. All other municipalities in Monmouth Count and the county itself use use either VHF or UHF analog systems. However, more and more agencies throughout the state are switching to digital systems and most, if not all of them have encryption capabilities and there is no scanner on the market that can decode encryption. Also, all 800 MHz systems (conventional and trunk) are being rebanded, so you should take that into consideration. The rebanding won't affect the ability to receive 800 MHz conventional systems, but it will affect trunk systems using 800 MHz frequencies. The reason I mention this is because the State Police use an 800 MHz trunk system
With that said, to satisfy your needs right now, you can purchase a relatively inexpensive scanner, like the Uniden BC246 (hand held/portable) for around $200 - 250 bucks or so, or the BCT15 (base model), same price range. However, they are not digital capable, but I believe, can be flashed to be able to receive the rebanded 800 MHz trunk systems.
You can also plan for the future and get a Uniden BCT396D (hand held/portable) or the base model equivilant, the 996D. These go for about 500 bucks. Both are digital capable, and can be flashed to be able to handle the new 800 MHz rebanding, which will take place soon. There are no municipal agencies in Monmouth County that use 800 MHz trrunk systems, but, as I said above, if you want to monitor the State Police, take the rebanding capabilities into consideration. 700 MHz systems may also begin to appear in the future, athough there hasn't been any mention, that I know of, of any being condsidered in New Jersey at the present time. I think that's quite a ways off yet, but both of these can receive 700 MHz systems, if and when they ever appear.
When considering digital, keep in mind what I said earier, that the the new digital systems, for the most part, all have encryption capabilities. Some municipalites that have them only encrypt some of their traffic, and others encrypt everything. People have gone out and purchased expensive digital scanners only to find that they can't monitor their local police because of the encryption. Some municipalities, especially in Ocean County, have only upgraded their police radio systems to digital and have left the Fire & EMS on an analog system. What any agencies in Monmouth County have planned for the future is a big unknown right now. There is talk about Monmouth County (the county itself) going to 500MHz trunk system and either of the scanners I mentioned would be able to receive without any problem, providing they don't use encryption.
So a few things for you to consider. And, I only mentioned Uniden scanners because that's all I own and have ever owned. Radio Shack makes some good products, bit I can't give you a lot of the specifics of the models they make. Maybe someone else can add to this.