Advance warning: apologies for adding more options to the list of possibilities!:
If it's for a 'scope that doesn't have an in-built 50-ohm termination, then a BNC T-piece can be used (attached at the 'scope end of course), along with a 50-ohm terminator. It's not great, but it should be adequate for a couple of hundred MHz (I did ask someone at Tektronix once, and they stated that was an acceptable thing to do on their MSO 2k series, which didn't have 50 ohm termination built-in). (And beyond a couple of hundred MHz BW, most 'scopes will have built-in 50 ohm termination anyway).
However, regardless, here is where a decent brand purchase makes a lot of sense (and it still won't be excellent unless you're even more selective since even branded BNC ones are often made to the operation level of old LAN terminators, I think!). On the other hand, Minicircuits, in particular, will have as decent BNC terminators as one can get for a reasonable price, e.f. BTRM-50+ is 11 euro at Mouser. That plus a T-piece would be an option anyway.
Yet another option (if a nano-VNA or similar is on the purchasing horizon one day) is to get a little SMA 50-ohm terminator, and an SMA-to-BNC adapter piece, and a BNC T-piece. That way, you only have to spend the Minicircuits-level budget on one part (the 50-ohm terminator) and you can use it with both the 'scope, as well as with typical SMA cables with the Nano VNA.
(EDIT: and if you're making your own terminator (or feed-through termination), then as @mawyatt says, two SMD 100-ohm resistors in parallel (but at 180 degree positions, i.e. not placed together) is probably the best DIY way, soldered directly on the connector, no need for a PCB unless you can keep the inductance low for the termination, unlike that really bad PCB. Mechanically it could be an issue (e.g. cracking), so you'd have to consider how you achieve such an approach, but electrically, it's a very good way. The photo below shows the 180 degree placement as an example (ignore that they are 200 ohm resistors in the photo, they were used for a different purpose, they should be two 100 ohm resistors). The epoxy was the attempt to reduce cracking risk.