Mohan (Chinese: 磨憨, Lao: ບໍ່ຫ່ານ) is on the Chinese side of the border between Laos and China. You can cross the border on foot.
The timezone changes at this border. Going from China to Laos it becomes one hour earlier. Coming to China from Laos it becomes one hour later.
The border crossing closes for the night at 8.30pm Laos time on the Lao side / 9.30pm China time on the Chinese side.
On the Laos side the guards might come up with any number of reasons to squeeze an extra dollar or two out of you.
A Lao visa on arrival costs about 30 US dollars, depending on which passport you carry. There is also an additional 2 US dollar fee for this service as noted on a large sign.
There are black market money changers on the Chinese side. You may want to change enough money here to pay for your visa on arrival. There is a large duty free shop with official money changer on the Lao side which you can use after you obtain your visa. The building has a sign saying it's open until 10.30pm, but it seems to close earlier.
If you cannot pay in US dollars you may be overcharged. In 2015, Hippietrail was told 250 yuan for the visa although the true exchange rate would be 205 yuan, but managed to haggle it down to 220 yuan.
On the Chinese side there are many places to get a big feed for a small price. Then continue walking along the highway out of town, after which you'll soon get a ride to the first city, Mengla, from which you can continue on to Pu'er, Ning'er, and eventually the relaxing capital of Yunnan, Kunming.
You might consider heading to Jinghong, the main city of Xishuangbanna, which is an autonomous area for the Dai ethnic minority who are related to the Lao and Thai peoples. It is however tastelessly overdeveloped for Chinese tourists to whom it is marketed as a local alternative to Thailand. Go if you are lucky enough to have a local Dai driver who might offer to introduce you to the true local culture.