first off let me say this, I am shooting for fun only. right now I have two ranges I can go to one is 100 yard public range and the other is about 900 yards private farm that can go to time from time.
so I want to try and keep cost down as much as I can so i can afford to shoot more.

1)  what powders do you all use and where do you get it from?  right now I am using two powders one is trail boss and the other is H50bmg.  The trail boss works good for very mild loads and is not bad on price but I don't get lot of performance  only about 1627 FPS with a 647 gr bullet. the H50BMG is expensive and would like to get some less expensive but with in same performance range (i load 200 grs of it under the 647 gr bullet)  

2) primers Right now I got some tula primers and love them for the price you can not beet them but  right now I can not find them any more, anyone know of a place to get them? The CCI primers are almost twice the price, and as said I am trying to keep the expense down as much as I can.

3) I have an open box of Barnes  50 caliber 647 gr XBT bullets that has 28 in it. ( 20 from this box and 8 from an other box) I really don't have  much use for this style of bullet and don't want to just waste it shooting into a dirt back stop.  If I where to list them for trade for other style of 50 cal bullets, what would be a fair trade for them? 1 of the barnes for 2 of API,  one for one for full Ap or the blue tip.  3 tracers for 1 barnes?  something like this be fair for both parties or are they worthless and just go and shoot them as I would m33 bullets?

Been using wc860 with good luck. Cheap too. Only with ball and AP. Saving my H50BMG for the match rounds. Was told reloader 50 was pretty good, not as hot as H50. If you go with wc860, work up to find the sweet spot. I made it up to 220 gr but the primers were a little flattened. Since these are more plinking, decided to just load 215 - 218gr. Easier on barrel wear. Mine has a 22 inch barrel to you may need more if your barrel is longer.
http://www.gibrass.com/gunpowder.html
http://www.patsreloading.com/patsrel/prices.aspx?category=Powder
Just to give you an idea on price. Google fu will help you find some.

where do you find loading data for the pull down powders? I have been thinking about getting some from http://www.gibrass.com/gunpowder.html but scared because no real published data for them and how would one know if the  pull down is mixed with other types of powder, or with this slow of a powder it really densest matter ?

You will have to ask online for load data. You will get what you ordered so no worries there provided its from a reputable dealer. There are a few of us here that can guide you on load data. Always start low and work up as each rifle is different. It may be cheap powder but it works.

i am looking at the jug of WC870  from http://www.gibrass.com/gunpowder.html

anything I should know before I buy a jug?  as stated it will be with 50 bmg and m33 bullets.

Get just 1 to see if you like it. Start at 205 gr and work up. Should be real close to wc860 but maybe do a search online to see what others say about it.

I too would recommend WC 860 Surplus powder for general shooting. I load it for ball, API, Blue Tip, and 690 black tip AP. I also load IMR 5010 surplus for Tracers and 690 AP. Surplus 50 powders will vary a little in burn rate. Common start charges for 640-650 range bullets is 205 grains with most shooting 215-220 grains of WC860. I'd start at 200 grains with 690-700 grain bullets and work up. My favorite load with 647 ball is 218-220 grains of WC 860. One lot of 860 I've bought has been slower and I can load it to 225 grains or even higher. A chronograph is helpful. Save your H50 bmg for match bullets. Since you only get around 32 rounds per pound, buy as much surplus as you can afford or that you will shoot for a good while so you don't have to work up loads EVERY time you buy a different lot number of surplus. Only 250 rounds or so from an 8 lb. jug. When working up surplus powder loads do it in larger increments like 3 to 5 grains at a time and when you get best accuracy with no pressure signs you could play around with minor increments to see if it would help.