A wise man I worked for at a software house used to like to tell customers "You've got three choices: fast, good, and cheap. Pick two."
Finishes are much the same way. In terms of raw material, most finishes are relatively inexpensive. Time is more the issue, which impacts cost most dramatically. If you're doing it for yourself, then you often don't care so much about time. So, then it becomes a matter of tool cost. A wipe-on sort of finish like the various "oil" stuff is easy - you can use inexpensive cloths. But, it's not very durable. You'll tear it up in no time flat. Stepping up to a spray rig will cost you some money, but you can shoot lacquer. Very nice finish, but a lotta work and time to get it right. Past that, you could shoot poly, which is the best, but you really need a dedicated spray booth with all the attendant costs.
The way I look at such things is you have to decide if you're going to to do it more than once. If so, then it's always cheaper to buy the tools to do the job properly and do it yourself. Be prepared to screw up - everything has a learning curve to it - but the rewards are fantastic. A good nitro finish will cost you at least $300 from anybody who knows what they're doing, but you can do it yourself for around $50. All the money in those jobs is in labor, not material, and even at that most guys are doing a labor of love. The amount of effort that goes into a good lacquer finish puts a $300 job in the range of minimum wage or less.
The various "oil" finishes are relatively easy as far as tool requirements, but the end result is pretty flimsy. If you work hard enough at it, they can look fantastic. I've seen some pieces on this board that were just stunning. But, it's a lotta work, and it won't last. On the plus side, you can do one even in an apartment.
Sprayed catalyzed poly is the best but is pretty much out of the question for the vast majority of people. It's toxic as hell, requires a very clean atmosphere, etc. You really need to be in that business in a real way to do it right. For what Warmoth charges for a finish, it's a bargain and a half.