On TV this question has been posed a few years ago, with limited results.

In the hope that new information can be supplied, the same question is being asked, again.

I have googled and perused hotel booking sites such as, Agoda with mixed results. However, those people with advanced web searching techniques are welcome to try, and please post their findings.

I would appreciate poster's experiences regarding guesthouses and hotels between the three hundred to five hundred baht range.

I know that they exist but finding them with limited Thai reading skills is a challenge.

guesthouses and hotels between the three hundred to five hundred baht range.

don't think you'll find those sort of places on hotel booking sites !

these are the ones you stumble upon out in the middle of nowhere on a road trip.

Just take a camping mat and sleep on the side of the road even better the nearest temple..beware of the dogs though.

you can usually find the cheap type of hotels in most city's usually in the town center or by bus stations talk a walk and look

Opposite the bus station in Saraburi is a hotel, been they  for a lot of years ,as for the price  I would not know but I would say ,it would be more than your 3-500 baht   range , as  would be most hotels in town ,ask  one of the motorbike taxi  lads at the bus station  they would  know, and will take you there  to.

Or ,or ,you could  go 50 km up the road  to Lopburi ,where they are cheap hotels ,in the  city centre   ,opposite the old palace ,is one .down  the road  from the palace towards the train station is a backpackers hostel ,that  will be cheap for certain ,there is a regular bus service  Saraburi-Lopburi, plus a regular white knuckle  minnie    bus, service .(  just an idea ).

There is one called Charoonrat (Spelling) opposite to the rear entrance of Tesco Lotus. It's around the 550 bht range. I stayed there for a few weeks when looking for a house there. TV, Fridge and that's about it'. But the place is very clean. 

Google Earth  14°31'27.32"N - 100°55'16.31"E