i have a 55 gallon res.. i use the smallest one of those chillers.. i keep it set at 67.. and my water stays at 70 or below.. even when the room itself is in the 90s and i have my air stone going...
If wherever you are located has a store that caters to marine aquariums, go check it out. Many of these stores sell used chillers at a GREATLY reduced cost in lieu of buying a new one online. You can also check marine forums for clubs in your area - that is always an easy source for used chillers.