The only discounts that I know of for older Daz content like that would be the 30% discount on Daz Originals that you get for being a member of the Platinum Club.

If you only ever intend to buy V4 and M4, that's a discount of 17.94 which doesn't cover the cost of a quarterly membership ($24, I think). Though you will also get a $6 coupon every month that you can use on Daz Originals. So you could buy V4 with the PC membership and get the discount on her. Then buy M4, use this months coupon, and get the PC discount on top of it. For a discount of: $8.99 + 8.99 + 6.00, which covers the cost of the PC and you have a PC membership for 3 months.

If you are going to buy the morphs for both characters (and you probably will, unless you're going to make your own), that's another $60 (and another discount of approximately $18). If you wait until the next month to buy them, you can use the montly coupon to reduce the price.

Sometimes Daz Originals go on sale and give additional discounts. Sometimes the PC membership goes on sale. Alas, you just missed a sale on the PC membership. 

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PoserPro 2014, PS CS5.5 Ext, Nikon D300. Win 8, i7-4770 @ 3.4 GHz, AMD Radeon 8570, 12 GB RAM.