I asume you mean invention sets 
You might take a look at Mids herodesigner, its a very accurate wy to see wich set fits in with power, together with the bonusses comming from the sets. Some prefer a bit of resist/defence, others like mez-resist, or just want the 'chance of X damage' or %-regen.
As for prices, 20m is a bit overdone, but some sets are only obtainable by TF's and sortlike, so being quite rare. Add the fact they are needed by nearly everyone, prices tend to go up massive.
The money itself, once you go from 40-50 the inf-gaining is insane, specialy at 50 all you get it influence. This way you can earn quite some cash by just wacking mobs and often be lucky to get the basic IO recipes that go 100-180k each.
50)Sinergy X/(50)Mika.
(50)MaceX/(50)Encore
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Does anyone know any Good Sets i should be looking to buy for my blaster, i have 2 at present, explosive blast, both in explosive what should i go for and whats the price range? i really dnt see how everyone gets so much money, people throwing around figures like 20 million, that must takes ages to reach, unless there is something i do not know?
cheers, wicked