This is a reasonable question if you're new to the gaming industry and don't yet understand how it works. The question reminds me of when I was a studio producer and would spend 8 hours with a band / singer recording a 5 minute long song and another 20 hours mixing, and I was always amazed that the engineers I worked with could work so incredibly fast. Meanwhile, some people think a 5 minute long song literally only takes 5 minutes to record. If you don't know, you don't know.
The type of game it is, is completely irrelevant. It's all about the design and art. This conversation about houses and contractors... it's like asking how much a house costs and the house could be a mansion, a ginger bread house, a doll house, the White House... the customer doesn't know the difference. Faxion Online which used the HeroEngine took a little over a year with a little over a dozen people. It also shut down as soon as it was released. If they each got paid $50k a year, there were 17 of them working for 15 months, that's over a million dollars. Pretty damn cheap. The other extreme, SWTOR with a few hundred people that cost over $300 million.
Outside of the HE, you can make a 2D game with mediocre art and program it in Flash. Maybe two people(artist and a programmer) could do that in a year for about $100k for both of them if you got new people just starting out. That will get you a mediocre game with a lot of bugs and problems on a 3rd party hosted website that will crash if you get any decent amount of traffic.
If you're talking about doing something in the HeroEngine, a few scripts won't change much. I'm pretty sure every single developer here is gutting the entire system and replacing hundreds / thousands of scripts with their own. You're not going to do that over a weekend. You're looking at a team of 2-20 developers getting paid around $50k a year(double that if they're in a big city) each working 1-4 years. And that's just the programmers. You'll need artists(concept artists, texture / graphic artists, modelers, technical artists, animators), audio people, designers, and testers.
The bottom line, if you think a quarter of a million dollars to make a simple MMO is laughable, I agree, but for the opposite reason.