When you say you're looking for the cheapest company, are you looking to book a package with a villa included? My advice would be to book the various components separately - loads of us do it, so we can help you out. The problem with booking a package, is that you're likely to get your villa allocated on arrival which means you won't know in advance what it looks like, or where it is.
My preference is to book directly with an owner, but others feel safer booking through an agency or management company. I've always felt that I get far more attentive service by dealing one to one with the person who has the greatest interest in making sure things work out for me. Most owners are people who've bought their dream holiday home and are renting it out as a means to an end. Whilst you do need to make sure that the owner has a management company to deal with any issues locally, I don't see any benefit in booking through one - you'll just pay a premium.
If you Google "Orlando Villas", you will get around a k-zillion results. They will fall broadly into three categories:
- Owners' websites for individual villas;
- "Hosting" websites on which owners pay to advertise their homes, but you still end up dealing with the owner. VRBO, Villas 2000 and VR360 Homes (along with some of the other links provided by previous posters) are all good examples;
- Agency websites - they are the middle man between you and the owner. Your contract will be with the agency and you won't deal with the owner at all. Whilst I wouldn't normally choose this route, good examples here include Florida Leisure and All Star Vacation Homes. Florida Leisure is a small company run by an ex-pat Brit. I have rented through them once and they are top people to deal with and look after "their" homes (i.e. the ones on their books - they don't own them) very well. All Star Vacation Homes is a slightly bigger concern. I've never booked through them, but I have stayed in homes managed by them and they have a good reputation, although I consider their prices a bit on the high side.
You'll also need to consider location. Generally speaking, the closer you are to WDW, the higher the price. The closest are those communities just to the south-west of WDW property and they include some of the higher quality sub-divisions such as Formosa Gardens, Emerald Island, Acadia Estates, Windsor Hills and Windsor Palms. These are the ones for which you'll pay the highest price and they tend to be the larger homes - up to as many as 7 and 8 beds. There are also some less expensive (although still very nice) options in that area - Oak Island Cove and Indian Creek spring to mind. There's another cluster of communities to the south-east of WDW properties along Poinciana Boulevard. Then there are scores more along the US27 from the point where it joins the 192, right down to Haines City. If you found a home near the junction with the 192, you wouldn't be too far away at all, whereas others could be a half-hour drive.