The options here are like options with your cags, and prices vary depending on the performance that you are looking for.
Ankle seals can be velcro, latex or even full socks sewn in. Waists again can be velcro, neoprene, and single or double waisted. There is also the choice between salopettes and normal trousers.
The type of pant you need depends on a few factors: - The type of paddling you are doing - The weather-conditions - How dry you want to stay
For white water and serious touring a pant with some kind of seal around the ankle is generally required. This may take form as either latex or a full sock taped to the bottom of the trouser. The advantage of a sock is it keeps your feet 100% dry allowing you to wear comfortable warm socks underneath. The downside is they are exposed to damage and you must be very careful to wear shoes with them at ALL times! Latex seals are good value and are less exposed than socks. However, your feet will get wet and in the coldest of conditions this can be uncomfortable.
Pants with a dual waist or bib are also a good idea for serious touring or white water, as when combined with a dual waisted cag and spray deck they provide an excellent (if not completely dry) seal around your waist. The more expensive pants will also have reinforcing over the high wear areas, increasing durability and extending the life of the product.
For more recreational paddling, such as sit on top kayaking or canoeing in nice weather where the aim is to keep off wind and spray, pants with a velcro closure at the ankle will be fine. These will do a good job of keeping the elements out but be warned, in a total immersion they will let quite a lot of water in. The plus side of these is they are generally lighter and less expensive.