I just got a recommendation from Andreas for a German / Venezuelan trekking guide company Kamadac based out of Santa Elena in the Gran Sabana.
Looks good.
For those who love to hike, the Roraima Trekking is one of the highlights of Venezuela. The tablemountains belong to the oldest rock formation in the world. During millions of years they have been formed. Most of the vegetation you find there, grows only at the table mountains.The Roraima tepui is the highest in Venezuela. Bizzare stone formations, barren rock landscape and unique plants shape the landscape. A three day tour brings us up to the Roraima. On the top we make a day excursion and visit the valley of crystals and the place where three countries meet “Brasil, Venezuela and Guyana.”
This tour can made any time of the year. During the rainy season we recommend it in combination with a boat trip to the Angel Falls.
Duration: 6 days
Daily walks: 3 to 7 hours
PRICE PER PERSON : 520 EUR (2 persons), 470 EUR (3 persons), 295 EUR (4 persons), additional day 50 EUR
besthike Roraima information page
besthike.com 
A great place to stay before starting your Roraima trekking trip, safe extremely comfortable and friendly https://www.airbnb.com/rooms/2896974 since you can book the place from airbnb.com you can rest assure you can get your money back if anything does not go as plan 🙂