I thought I'd just add a wee note to let you know where I get my promarkers from, I have found the best deal from Angela at Angel Crafts who, as well as selling the 5-packs, also sells larger packs, and singles - and the best value bulk buys I've found in the UK.
If you are just starting out with promarkers I would recommend the skin tones pack containing Ivory, Satin, Blush, Dusky Pink, Cinnamon, its an absolute must for your collection.
I personally, would recommend buying 3 colours from a colour family and that way you can pick and choose which and how many colour families you buy depending on your budget
I am going to list some selections that I would recommend for beginners and those on tight budgets, I have selected them especially for easy blending and giving as wide a scope as possible with a limited number of pens.
Browns: Sandstone, Cocoa, Burnt Umber, Umber (the 5th colour, cinnamon is in the skin tones pack)
Oranges: Apricot, Pumpkin, Mandarin
Yellows: Pastel Yellow, Mustard, Canary
Greens: Meadow Green, Apple, Grass
Blues: Blue Pearl, Cornflower, China Blue
Purples: Lavender, Lilac, Amethyst
Pinks: Blossom, Rose Pink (the 3rd colour, Dusky Pink is in the skin tones pack)
Greys: Warm Grey 1,3, and 5
So for instance you could buy the skin tones plus the browns, greens and blues all for a total of £15.95 (bulk buy) + £7.45 (skin tones) = £23.40
I hope this is of some help