My hex I got used, no filter or anything came with it. I got it cheap because the light didn't work. And it got busted, but I still use the hood it had to light a standard 5.5 G, and it does a fair job, though there are those two cut off corners in front that don't get as much light. So far, doesn't seem to matter too much.
I usually try to get bulbs that are rated at least 6500 K. I don't care if they say they're good for plants or not.. I just want that K rating. It works. I don't have Petco stores, I don't think they're in Ontario, we just have Petsmart. I am not sure what they'd have that would work but if it uses a standard size of aquarium tube, you should be able to get a 6500 K tube that will work in it.
If possible, you might try to get a small shop light or utility lamp with a reflector. I think the smallest shop lights are two feet long and you can certainly get 6500 K T12 tubes for them. I would guess they'll eventually be replaced by T8 tubes. The clamp lamps I've used for tank lighting are not costly, and you'd get all these at a place like Home Depot. The clamp lamps have an 8 inch, or in some cases maybe a 10 inch, round aluminum reflector, and take standard screw base bulbs. Just get Daylight type spiral bulbs, rated at 6500 K, and for a 5G, I've been using a pair of them that are, I think, 13 watts each. You can get an adaptor that allows you to put two screw in bulbs in one socket.. they work with the 8 inch and 10 inch utility fixtures. If you put in two, you'll have quite strong light for a 5G. I use one of these on top of my Betta tanks, 2.5 G, it sits right on the tank rim, with an 11 W daylight bulb in them. Grows anubias, moss and Hygro difformis very well, and some frogbits too. Though the frogbits are temporary, I'm selling them next week. I hang the lights from anything handy and have built holders for them out of electrical conduit, the grey PVC kind. Or you can take off the clamps and just put a wire bail on them to hang from some sort of support. I like making my own gadgets more than buying new ones, though I have to say the newer aquarium lighting is pretty nice looking.
Btw, Bettas shouldn't freak out because the light's on. They don't see their reflections in the glass from inside the tank, it's an optical illusion that we see looking in from the outside. Unless there is a mirror he can see himself in ?
I have my 2.5 tanks side by side with Bettas, and just a piece of plastic mesh between them to make the view less interesting so they don't flare all the time. I pull it out every day or two and let them get some exercise making nasty faces at each other for awhile.