If you are limited at this point, funds wise, and still want to help him here is a suggestion.. something I do since I have multiple bettas and not willing to spend hundreds on each tank lol..
(btw, a 1 gallon is suitable home as long as the weekly water changes are made and the temp is correct)
Petco- Kritter Keeper
It doesn't look like much- but it can be. For about 10$, a little over 3 gallons you can get the large one. They are safe to heat and plenty of room to decorate. It doesn't look clear in the picture, but they are- I have a few of them myself.
You get one of those, a 15-25 watt heater, a desk lamp (40 watt bulb is what I recommend, as it won't affect the temp of the water, nor will it melt the hard plastic lid). All of that should be less then $40, the lamps you can get for under 10$ at Walmarts, heaters under 25$.
For substrate and deco, check around craft stores before going into specialty stores, or even Walmart- you can get the glass rocks much cheaper at smaller stores. Big Lots has some in the candle aisle for only a couple dollars, and you get twice as many as the small bags at pet stores.
As far as your heat lamp question goes.. it's not a heater and won't work as a heater for the tank, so you will have to buy a heater appropriate for the gallons, roughly 25watt. Some people seem to have problems with the filter, being messy/loud.
Here is one you can order from Walmart, has almost 200 reviews and the reviews are good.. and cheaper then the other- if you order it online it may come out the same.. but it's an option. Hawkeye 5 gal