Stroking depends on a number of variables, but for the street rodder, you really shouldn't go more than a 6.00" connecting rod in a 350. The benefits above that number are so small and such a financial money pit, it's not realistic unless you go with another displacement block completely.
The factory 5.7 inch rods and crank produce a 3.48 inch stroke. You can retain the rods and change the crankshaft to say a 3.75" stroke, but either way, you'll have to change pistons. The wrist pin location is what gets affected and that should be taken into account. Another thing that will need to be verified is block clearance for the rod and interference relative to the camshaft. I think Jack or Mike(vigman) recently posted his clearanced block.
Here's a site on explaining some of the things that need to be taken into account when choosing
shorter vs. longer rods.
Under the thread I posted in this same forum titled, "Bad A** Advice, it is suggested that the cost of building is paramountly related to strength.
There are too many variables to put a single price on an engine, unless it's a generic "crate motor" and there are lots more options that dictate how strong an engine will be and what it will cost. Always remember, it's the strength you're paying for... not the horsepower.
Having said that, you could go with second hand items. However, since you live in Sweden and couldn't view the parts yourself if bought overseas, I would highly recommend against from buying here. Some people are honest, some are looking to rip you off. So it's 50/50 when buying unseen on used parts. At least with new, you know what you are buying from a reputable company. Again though, if you have a claim, it's going to be difficult and a long process with shipping times and such. If you want to take a look at some websites for comparision purposes, let me know and I'll list a few.
--Bullitt