What are your needs?
If you plan on needing to rely on this GPS some day, get a dedicated unit. Dedicated units, unlike smartphones, can take a knock, get wet, and with a set of Lithium batteries can be relied upon to power on.
Do you want marine maps? If yes the first point will be sure that the unit you select supports your inland lake. Garmin has a good selection of inland lakes in their map database. Often maps can be added to a device, but that cost about $100. It is normally a better deal to by the model that has the maps included.
If the unit is for more casual use, you can go the smartphone route. Navionics has the best inland lake support. Look into getting a good waterproof case, like the Lifeproof. If your phone has GPS, there is no need for cell service for the location service to work.
Are you looking for a basic unit that just shows Lat/Long? PM me and I'll send you one for the cost of shipping. I've been in this business for a while and have a box of the things.