If low purchase price is your main concern there are a lot of inexpensive burners to be found. Inexpensive usually means Chinese or east European manufactured. Most Chinese stoves are of a more traditional style and fabrication (cast iron) where as the east Europeans tend to go more for steel fabrication and more modern styling. Quality can be variable but the following are all inexpensive stoves with all the relevant certifications that I would expect to be trouble free.

Clarke	Kings of the cheap stove, quality has consistently improved over the last few years, Chinese made, with the added advantage you can visit one of their nationwide showrooms and usually walk away with you choice. www.machinemart.co.uk
Capital Sirius	Really nice stoves with a lifetime guarantee. I believe they are Chinese manufactured but  I'm not certain. DEFRA approved, I've fitted a few and rate them highly. www.capitalfireplaces.co.uk
Ekol	The Ekol Clairty range are quality affordable burners. The range is all left handed. I retail Ekol stoves
FDC	I'm fast becoming convinced there is not much on the market that is better value than FDC freestanding and inset stoves. Steel fabrication with cast doors, they don't permit web based advertising of their prices but they are not dissimilar to Firefox. DEFRA approved, high efficiencies (i.e. over 80%). I retail FDC stoves
Firefox	Chinese manufactured and British styled and designed, I've fitted more Firefoxs than any other stove. Never seen a faulty one, the model 'T' of the stove world. DEFRA option.
Fireglow	Chinese budget stove, good selection. DEFRA option. www.fireglowstoves.co.uk
Grey Metal	I'm impressed by the price of the Cube and the totally over the top engineering of the Nero. Made in Bulgaria fabricated from German steel, I use a Nero myself. If only they were DEFRA approved. Quality is not usually this cheap. I retail Grey Metal stoves
Saltfire	Ticking just about every box Saltfire's ST1 and ST2 stoves are fantastically good at everything they do (efficiencies over 80%) and at a price to take note. I retail Saltfire stoves
Sunrain	Chinese made budget stoves of respectable quality. Sold in the UK under a number of other brand names including Fireglow and Firefly? www.sunrainfireplaces.com
Tiger	Quality Chinese made cast iron stoves. Distributed in the UK as part of the Gallery Collection. They claim to be the UK's best selling stove, interesting optional cook top. DEFRA option. www.galleryfireplaces.co.uk