Which SSD to buy?

A ssd will transform the performance of your laptop.
I have replaced the hard drive on everyone our family owns.

I have a method to pick between equally performing products.
Go to Newegg and find the candidates.
Filter on the reviews by verified buyers.
Then look at what percent of the reviews have zero or one eggs indicating some sort of a problem.
In particular, look at the reasons for a bad review. Some are not very valid, so exclude those.

Today, I would not buy anything but Samsung, or possibly Intel.
Samsung has a nice free ssd migration app that will copy your hard drive to one of their ssd's.

Do not be much swayed by vendor synthetic SSD benchmarks.
They are done with apps that push the SSD to it's maximum using queue lengths of 30 or so.
Most desktop users will do one or two things at a time, so they will see queue lengths of one or two.
What really counts is the response times, particularly for small random I/O. That is what the os does mostly.
For that, the response times of current SSD's are remarkably similar. And quick. They will be 50X faster than a hard drive.
In sequential operations, they will be 2x faster than a hard drive, perhaps 3x if you have a sata3 interface.
Larger SSD's are preferable. They have more nand chips that can be accessed in parallel. Sort of an internal raid-0 if you will.
Also, a SSD will slow down as it approaches full. That is because it will have a harder time finding free nand blocks to do an update without a read/write operation.

You definitely want to look at SATA 3 SSDs. SATA 2 is old and outdated by now, and most modern SSDs, even budget ones, can max out SATA 2 interface without problem. Looking at your budget, it's pretty tight for a 240GB SSD.

The only SSD that I can think of that is that cheap is probably the Trion 150 or PNY CS1311, which aren't unreliable or outright horrendous SSDs. The Trion 150 just has abysmal Random read/write performance compared to other SSDs. The performance gain that you see going from HDD to SSD is mostly because of the better random performance of an SSD when compared to an HDD. The Trion 150 is just a bit above a good HDD (It's better, but not by as much as expensive SSDs). The CS1311 is basically the same in performance.

Overall, you get what you pay for. An 850 EVO is just so much better than both of these budget options, and the cost reflects that. If you really want to feel proud of your purchase, I'd recommend waiting till you can afford it. Also SSDs to consider (which I haven't looked at reviews for yet) are Intel 540s and Samsung 750 EVO, which are new budget offerings from Intel and Samsung, the two big players in SSDs.

Anandtech benches SSDs pretrty often, and their reviews have a nice collection of data points there for you to see how different SSDs compare.

OCZ Trion 150 review
PNY CS1311 review

tl;dr:PNY CS1311 is the best available in your buddget. Check out Anandtech's reviews to see a good comparision of available SSDs. If you can save up a bit more, you're gonna see much better results.

Edit: I wanted to clarify when I say that the Trion 150 and CS1311 have bad random performance, I don't mean that compared to HDDs. You'll still see noticeable improvement moving from your HDD to an SSD. I am comparing those SSDs to better not-so-budget SSDs.

The SP550 is in the same class as the CS1311 and Trion 150 that I mentioned above.
Review on Anandtech

I totally understand the data reliability argument if you're using the SSD as your primary data storage device.

What I have done on my laptop, for that very reason, is put in a cheap SSD as the boot drive. I put windows and all my programs and games on there. Basically everything that I can easily reinstall goes on there. What do I do with the rest of my data? I replaced the dvd drive with a hard drive caddy and put the original hdd in there. I keep the recovery partition and all of my personal data on the HDD. This means that I get the performance boost of a cheap ssd where speed is important and the reliability of magnetic storage where my data is.

IIRC the Q300 is TLC. If you really want very high data reliability, and are willing to spend more for it, I'd look at Intel and Samsung's MLC offerings.
The Samsung 850 EVO and Intel 535.