I would say, this depends on the embassy/consulate where you get it from. Swiss consulate, where I got it from, required an onward ticket within 60 days.
Because in Bangkok the immigration is annoyingly far out of town and it can take hours to get things done there. So instead of paying for public transport and taxi, you pay the hospital and save some time :)
I've used the service once. That time the fee was 600 Baht. I didn't have an appointment. Just went straight to the 10th floor in early afternoon and dropped off my passport. They filled in the form and charged me in advance. The next day I could pick it up.
I went there in January. Here's how it worked out for me. Took it from a report, I wrote before.
I picked up my passport at around 3.30pm. The queue was already at number 570, so I got my passport immediately. Outside of the embassy I took a van to the border for 200 Baht (50‘000 KIP). At the border I had to pay a fee of 11‘000 KIP, because it was after 4pm. This counter is before immigration (today it was hidden by umbrellas) and you will get a card that you will need behind immigration. Laos Immigration was quick. Behind immigration I was offered a taxi to Udon Thani airport for 1‘500 Baht. I asked for a van and they said, I could sit down and wait. I opted to take the shuttle bus for 4’000 KIP (20 Baht) and to go through Thai immigration first. Took about 40 minutes to go through there. If possible, have a Thai arrival card already prepared, so you can save some time in the queue. After immigration I could hop on a van that had one seat left. It took about 1.5 hours to the airport. Udon Thani airport doesn’t have much to offer. There’s one local restaurant in Terminal A and some fast food in Terminal B.
If you have a Tourist visa or a stamp under visa extension, you can always once get an extension by 30 days. So if you did a border bounce to Cambodia and entered again, you can get that extension.
FYI: My friend did not get a longer extension than the usual 30 days. He got a certificate from the hospital about the health condition of his girlfriend but at the immigration he was told, that they could not grant a longer extension. They recommended him to do a border hop to Cambodia. He did it at the immigration office in Nakhon Pathom.