You need to give us an idea on what you want to spend...
I have a Garmin Edge 200 which was great for what I wanted it for at the time basic GPS with crumb trail course, no maps, no HRM, no cadence. Cost me £79.99.
At Christmas I came across one of the Amazon lightening deals and purchased an Garmin Edge 500 which has many more features including HRM & cadence (if you purchase said sensors) and got that for £89.99 usually a lot more (£149.99 I think). My Edge 200 went to my OH whose Edge 705 is giving up the ghost completely.
If you want maps, then you will have to pay much more, but you will find other options available and
Amazon Lightening deals are a good place to keep an eye on.