What kind of beryl are you wanting to treat? The only heat treatment for beryl I can think of is heating aqua to drive off the green. If that’s what you’re after, I would consider leaving it as is if the green cast is at all attractive, as some like it that way (I do). If the green is brownish or too dark, treatment might be beneficial. With the cost of shipping and treatment, I don’t know if it would be worth your while. Unless this is very expensive rough or cut stones (really it should be cut before being treated), I would consider finding a local jeweler or craft center with a burnout oven you could use and do the treating myself. You put the stones in a crucible surrounded by sand, place them in the burnout oven and gradually raise the temperature to your target (the details are available on the internet). Ramp up slowly (~50C/hr) and then shut off the oven and let it cool until you can handle the crucible, sand and stones. If 400C is not high enough, go higher in increments of 25 to 50*, but be aware that you can get it too hot and loose all the color.
Bear in mind that stones can crack during heat treatment and any flaws may cause the stone to shatter or break. If the stone has a greenish cast, it may have already been heated but not be amenable to heating away the green. You can probably get away with heating to 400*C in an hour, but I gave a cautious protocol. Some folks will heat aqua nestled in some fiberglass wool in a test tube, where you can see the color change, but this is a bit more risky. Heat treating can be fun, as long as you’re aware of the risks.