I'm trying to rent an apartment for next year. The rent listed on the company's website is $150 less than the rental amount contained in the lease they've emailed me. I haven't signed anything yet, but I'm wondering what my options are as far as trying to get the rental price down to what is listed on the website.
You can ask them for the cause behind the difference.
They probably list the cheapest version of each apartment size. Apartments may rent for more if they have superior views, higher floors, different exposures, different layouts, better installed appliances, or better construction materials. It could also be out of date if they increase their rent regularly. I'm used to seeing it expressed as a range, but sometimes they give you the headline cheapest price.
Your negotiating position depends on the occupancy rate of the building, the neighborhood, and the city/region, as well as the particular market niche of that building. If you can get a better deal somewhere else, then you can say that to them if they are intransigent on price (only say it if you mean it).
Some landlords negotiate, but a lot of corporate managers are not accustomed to regular negotiation. You may be able to instead ask for an accent wall (painted a striking color) or free parking, if they won't move on price. But if they have almost all their units filled, then negotiating is more a courtesy than a necessity.
If you haven't signed the lease yet, you have one very powerful negotiating tactics at your disposal: Going someplace else. In a free market, your most powerful weapon as a consumer is the ability to walk away.
As others have noted, the first question is whether this is a mistake, if the advertisement was actually deceitful, or if you were fooled by a vague advertisement.
It's certainly worth asking about the discrepancy. Maybe they will reply, "Oh, we're sorry, that was a mistake", and that will be the end of it.
If the company actually lied in an advertisement -- if they said this particular unit with this size, this location, etc costs $X per month but then when you go to sign the papers it says $X+150 -- you might be able to report them to a consumer protection agency or sue them for false advertising. But if you haven't actually signed anything or paid anything yet, I wouldn't bother. Unless they're very stupid -- which is possible, of course -- they have some fine print somewhere that says that what they did is legal, you'll get yourself tied up in legal proceedings, and for what? Just find a different apartment and save all the trouble. I wouldn't get into legal proceedings unless they already have your money and now are trying to change the terms of the contract.
BTW, I would not want to sign a contract committing myself to a long-term relationship, like a lease, with someone that I was in the process of suing. You can't imagine that they will WANT to provide you with good service on Tuesday if your lawyer was just badgering them in court on Monday.
It's fairly common for advertisers to say "prices starting at $X" or "as low as $X". In that case you should take it for granted that the units at that price are going to be very low quality or otherwise undesirable, or why would they be the cheapest? In the case of an apartment, it's going to be the one that's smallest, or has the most inconvenient location, or has old barely-working appliances, or some such. On the one hand, if a company has a wide range of products to offer, you can't expect them to list the price of every one in an ad. On the other hand, companies often make one item that they know is so shabby that almost no one will actually want it, slap some super low price on it, and then use that in the advertisements. You could debate how honest or dishonest this is endlessly. If I was looking for an apartment and a complex advertised "$800 and up" and when I look at the apartments the one I want is $900, I'd probably say okay fine, it's the "and up". If it turned out they really had nothing decent for less than $2000 and the $800 unit is a closet with privileges to use the outhouse out back, I'd say it's a scam and go somewhere else.
I guess the other question is what other options you have. If this place is advertising apartments for $X and, whatever the story is about the advertisements, the unit you want is really $X+150, and in fact there are plenty of other apartments available that are $X or less, then just go somewhere else. If all other comparable apartments are $X+300, then this place is still the best deal and you may just have to swallow it.