I have unbranded ones off ebay, not had any issues so far and they are suitable for a much higher wattage than the branded products I was looking at for a higher price, think I paid about 4 pounds each. you have to wire them up yourself though. I prefer how they look in the viv too as they are really close to the ceiling. The link below is like what I use.
CERAMIC VIVARIUM HEAT BULB LIGHT LAMP HOLDER REPTILE | eBay