You need to decide if you will purchase or rent a devices. Either option has benefits and depends on your business or personal preference. Upfront costs for renting a device will be lower, over a long period of time, buying is typically cheaper. In volume buying several devices may reduce your costs.
The more often a device reports the the server the more data the devices uses. This affects both battery life and data usage. The more data usage typically the higher cost the data plan is. Finding the right balance between updates is key for maintaining long battery life and not paying to much on data.
There are many sizes of GPS locators, typically the smaller they are, the easier they are to install and use. The trade-off for smaller devices is less battery life and smaller antennas. Larger tracking devices are typically best used for tracking vehicles where smaller ones are for most other situations. Keep in mind the total cost of ownership when selecting a GPS tracking devices and include installation costs and maximizing their use by allowing for a wide range of applications.
Also when considering the total cost of ownership, remember that the benefits can easily cover the costs of the device. In the case of tracking vehicles you can reduce your fuel usage, improve fleet performance, increase driver safety, and deliver better services. If you are tracking assets recovering one expensive item can easily cover the costs of ownership. In the case of elderly, dementia patients, kids and pets, the cost of replacement is effectively priceless.
In some cases you can finds GPS tracking devices on ebay for under $20. In these cases they do not include a sim card and you will need to provide your own. Also, these devices are typically not easy to setup and use and quality is iffy. Be sure to choose a well built device that will not fall apart if gets hit or dropped. Choosing a device with bundled data is often cheaper as you are billed at a group rate rather than an individual. The costs for a month of data should be under $10 a month, or you are overpaying in most cases. Make sure if you using the device overseas that international coverage is included otherwise you could be hit by a surprise bill at the end of the month.