Difference

Estimate means to make a judgment which is based on general knowledge rather than specific facts. It can also specifically mean "an estimate," which is a price which someone gives to you, subject to change, for something they will sell you, or a service which they will provide.

Evaluate means to put a definite price on something, or to make a precise judgment of the worth of something. Unlike estimate, evaluate usually implies that the person who is evaluating something knows or can determine exactly what a thing is worth.

Reckon is more of a coloquial term (one which is used in casual conversation) and means much the same as estimate. It means, basically, i don't know, but this is what i think.