1

Get yourself to chiang Mai .Find yourself an expensive hotel or reasonable priced guesthouse .. Walk around Ch.Mai ,inside the old city wall . You will pass many tour shops ,pick up their brochures and peruse at your leisure over a nice cold drink .Select one of those, or one from the g/hse or hotel .
N.b. Sunday is walking street, my favourite day in that city ,keep 4pm to late ,tour free .

2

There are many freelance tour guides with their own car/van/jeep who can give you a private customised tour for around 1000-3000b ($30-90) per day depending on how far and if it's high/low season. You might start with the taxi that picks you up at the airport or train station, since many of them do tours as well, or enquire at your hotel/guesthouse. Anyone well-connected in tourism can usually produce a car/driver although in peak season Dec/Jan it can be more difficult to find someone who isn't booked out.

I can suggest some daytrips like the Doi Pui summit to Hmong villages, botanical gardens, coffee growing, trails, etc. The Samoeng loop road which passes waterfalls, scenic viewpoints, and a handful of tourist attractions in the Mae Sa valley then gets blisfully quiet at the far end of the loop, also between Sangkamphaeng and Doi Saket there is beautiful hilly country up and over the ridge to Chae Son national park with caves, hot springs, waterfalls, and nice walks.

3

^^ exactly what Captain Bob says.

We usually hire a car/driver/tour guide for day trips or exploring when we are in Chiang Mai. Our historical average is to typically spend around $50 on average for the service and then attraction fees on top of that. The price may vary a bit based on season, and usually mostly by the distances involved as the fuel is a fixed cost to them (and fairly high say relative to their time)