Cremation is not a mere acceleration of natural decomposition. Your flesh is burned away (some of it going into the atmosphere), and then your bones are pulverized.
In the Orthodox Church, cremation can be allowed by economy for a pressing reason, such as a body that is already mostly burned (such as a person who died in an accident by fire), an epidemic, or being in Japan where burials are simply not feasible for most people. However, cremation has traditionally been fully and fervently rejected as a desecration of the temple of the Holy Spirit, and those who deliberately choose cremation are usually denied Orthodox funerals. A priest with a dying person who demands cremation might not even say prayers by their deathbed, as their intention for cremation places them outside the Church. Cremation is not something to be trifled with.
Yes, cremation as a process is extremely disrespectful to the human body. (As is embalming.) While economia may be liberally distributed here in the West, the long-standing teaching of the Church is burial only, and like Orual said, in normal circumstances it is enough to prevent a Christian burial (and the prayers and final absolution that goes with it).
Economics and cost is really not an acceptable excuse for deviation from Church teaching. According to some brief Google checking, cremation costs range from about $1000-3000 (though it seems you can get subsidized ones from a cremation society for $500). Cemetery plots vary greatly (it is real estate, after all), but Arcadia, Florida
has them for $750. And if you're willing to do the legwork, you can petition your local government to have private property zoned for burial, and that would cost nothing.
So, cremation and traditional burial do not have significantly different costs. And we have loving parish churches—if someone can't afford to be buried, then the parish is there to help. We don't just toss each other to the wind at death. That is why burial is so important: the body isn't an empty wrapper, it is an integral part of the person, which needs to be cared for properly.We don't trifle with our spiritual lives in life, we shouldn't in death either. How much money in our lifetimes do we spend on icons, books, candles, potlucks, and the rest? Considering we're all going to die eventually, it is prudent to plan for our own deaths. We are doing so spiritually, so why not materially as well?
And if we can't, there are ample people around us, our family in Christ, who can step in to help. Burial of the dead is one of our Christian duties and acts of mercy for others, and it would be cold-hearted indeed for a parish to send a person to the incinerator because of something as silly as money.
And if a person is simply defiant and refuses burial because of some prideful streak, well, Lord have mercy on them. Their last act being a refusal to submit to the Church would be quite unfortunate and sad.
There are very few excuses, at least in North America, to not be buried.
(As an aside: If anything, more parishes should have graveyards on-site. There is a mission parish here, which has passed up several Protestant buildings because they prefer to save for a large piece of land so they can have a graveyard. That is most commendable, in my opinion.)