Once my ravagers show up in the mail, i'll have all the cards i need for an Affinity deck. So i was reading up on the actual rules for affinity, and here's what i stumbled across, that seems a bit wierd.

409.1f The player determines the total cost of the spell or ability. Usually this is just the mana cost (for spells) or activation cost (for abilities). Some cards list additional or alternative costs in their text. Some effects may increase or reduce the cost to pay, or may provide other alternative costs. Costs may include paying mana, tapping permanents, sacrificing permanents, discarding cards, and so on. The total cost is the mana cost, activation cost, or alternative cost (as determined in rule 409.1b), plus all additional costs and cost increases, and minus all cost reductions. If the mana component of the total cost is reduced to nothing by cost reduction effects, it is considered to be {0}. It can?t be reduced to less than {0}. Once the total cost is determined, it becomes ?locked in.? If effects would change the total cost after this time, they have no effect.

409.1g If the total cost includes a mana payment, the player then has a chance to play mana abilities (see rule 411, ?Playing Mana Abilities?). Mana abilities must be played before costs are paid.
This means if i have nothing but 2 lotus petals in play, i can announce playing Frogmite, since i have 2 artifacts in play, he'll cost 2 mana to play, then i sac the petals to pay that 2 mana...

Seems realy wrong somehow.
Can it realy work that way? Are Lotus Petals realy 2 mana a piece towards spells with affinity?