I ask because I would like to get some idea of how likely it would be to buy non-kosher tefillin on the web. Prices range widely. Various websites offer a bottom-of-the-line pair of tefillin for $150, $400, or $550, depending on the site. The high-end tefillin can run to well over $1,000. The lower prices are from websites that sell a wide variety of merchandise. Has anyone bought inexpensive tefillin on the web and had them checked? If so, what did you find?
I once had a pair of tefillin peshutim. I'm not going to mention the name of the company from which they were bought, because I don't want to spread slander about them. But let's just say, when you buy cheap, you get cheap. There's no such thing as good quality products for cheap prices.
One of the biggest issues with these cheap pairs of tefillin is their longevity. I'm not a sofer stam, so I'm unable to comment on the kashrus of the parshiyos, the battim, and the retzuos, but I can say that tefillin peshutim don't last long, no matter how good you are at taking care of them. The pair I had lasted about a year (and I was extremely careful with them). After that, the dye on the retzuos was peeling off, the battim were cracking, and the paint was chipping off them too. I finally had to give up on them completely when one of the sinews holding the shel rosh together just snapped.
These cheap pairs of tefillin are primarily being sold for those people who just want a pair to wear on their bar mitzvah, and then throw them in a closet and forget them forever. They're disposable tefillin, "Cracker Jack box" tefillin. They're very low quality, kashrus issues aside.
That being said, I managed to scan one of the parshiyos from the shel rosh:
You make your own judgment. Like I said, I couldn't tell you if they're kosher or not. But what I can tell you is something doesn't feel right about them. The parchment is too smooth. It doesn't feel real. And I'm being incredibly honest. They just don't feel right.
I'd save and spend money on a nice pair of tefillin, from a reliable sofer. It's a good idea to spend good money on a mitzvah. Think about it this way:
The price for the new iPhone Xs, with only 64GB, is $1,000. People actually spend this kind of money on something as meaningless as a phone. Why should tefillin, which connect you with Hakadosh Baruch Hu instead of other people, cost any less? And why should you spend any less?