To the OP: It is really up to you. If you really want one than go ahead. Let's say the average price for a P. metallica sling right now is $175. Do you really want to trade your slings away for $25 worth of credit? IMO I would keep the slings and fork over the extra $25 and you also don't have to deal with shipping (that's if it isn't a local trade). In the end it is all up to you.In my opinion, not unless you just have a bunch of extra money laying around. And because the simple fact that you are asking, I assume that you don't. There are so many other tarantulas that are just as beautiful for way cheaper, so I think the only reason to pay that much for any T is that you already have a <butt>load of common Ts and want to top off your collection, or you just REALLY personally like the species. Don't get me wrong, P. Mets are extremely beautiful, but I think 90% of the reason people buy them is because of all the hype & the "hey look at me, I've got a P. Metallica" syndrome. If you dont have a Versicolor, I would suggest getting one of those(just as pretty) and simply pocketing the $100+ that you would save not buying the pokie.
But enough of my rant, if you really want to buy it then yeah, thats an ok deal as far as P. metallicas go. They are typically $150-$200, so depending of what brachy slings you're trading, it should come out to right around that range.