Getting back to the $25 budget (still doable in 2016)...
The Planet Bike Rack Blinky 5 (and similar) taillight/reflector types still seem like a good value -- including the Serfas models that take AA batteries rather than AAA. The reflector does increase the nighttime visibility to vehicles (assuming they're not running dark), and the design has a wide angle of view. Not sexy but these combo taillight/reflectors are pretty good for $25 or less.
In comparison I just got the Cygolite Hotshot 50 ($30 at REI) hoping it would be bright enough for daytime use, but it's just adequate in daylight and then only within the narrow aperture of maximum brightness directly behind the typical Cygolite Hotshot narrowly collimated beam.
Overall it's no better than my $15 Planet Bike Rack Blinky 5, just different. The Planet Bike rack lights combine LEDs and reflectors, so it has decent visibility across a wide angle of view. The PB has a somewhat narrow aperture of maximum brightness but that primarily affects the viewer's elevation, not lateral position. The Cygolite has a narrow aperture of maximum brightness that's much more position sensitive.
I suppose I'll keep the Cygolite since I needed to replace the balky old lights that came with my '92 Univega. It's still an improvement over those much older LEDs. And it is very bright at night, with a good selection of flashing and steady modes to suit personal tastes and local etiquette. But I won't rely on it as a daylight visible rear light.
The 20 year old LED tech taillight/reflector on my Univega is getting glitchy so I'm going to replace it with the Serfas TL-STP because I like having that combo taillight/reflector on the rear racks. And the AA battery should run for weeks or months between battery changes, considering how seldom I need to change AAA batteries in the Planet Bike blinky. The Serfas is only $25 or less.