No one knows what is needed for a funeral or what it should cost ahead of them consulting an undertaker when a loved one dies.
There's nothing stopping you making enquiries in advance - whether on a thread like this, asking those who've already organised funerals and know their own costs, or just approaching the funeral director of your choice. The one I had to use recently gave me a comprehensive brochure of most of the costs, but I was free to ask about anything else - there were absolutely no hushing sounds and telling me that 'it's disrespectful to ask about costs' or anything.
We tend not to research it until the time we need the services, after a loved one has died, but you could very easily go into/call/email any half-decent FD (or all of them in your town) and tell them you're planning in advance - whether for your own or an elderly/very ill relative - and would like to know the options and breakdown of costs. Of course, costs might change over time, but you'd still have a reasonably good idea.
As the PP said, we spend so much time thinking, planning and costing up weddings in advance, but we hardly ever do the same for funerals; but there's absolutely no reason why you shouldn't or couldn't. It's our own fault (and I include me in that) that we don't usually bother to do it. We can't blame the FDs when they're right there in premises that are open to the public and, like any other business, very happy to give you information that could well lead to you spending a lot of money with them in the future. Any FDs that won't do this or are cagey are still helping you, as you then know to strike them straight off your list (and tell your family).
Good, reputable FDs will only be discreet about in-depth (even graphic) details out of respect for your own sensitivities at an emotional time - and as has been said by a few people upthread, some bereaved people prefer to leave as much of it as they can to the FD and not to dwell on the details; but if you have gone to them in advance and you come out and ask them about all the specific costs and what the different services entail/include, they've no more reason to be coy about discussing their everyday service, products and prices with you than a greengrocer would be if you asked the price of a sack of potatoes.