Are spiders still the go-to budget deck? I managed to get some lucky drops(extra sheoul mark/couple nefari messengers) to net me some runes on poxbox and i noticed that quite a few core runes in the deck run pretty high on the pricetag. (phase spiders, soul crawlers, arachnablades)
Spiders are still excellent for cheap, yes, though you may want to consider Fire Amp, as it's not overly expensive either.
You have to get at least some exos in your bg. You would only need klzik which is free and x2 phase spiders. Haven't seen anyone use the void spider but since he's easier to get now. Either way klzik and bunch of rares-commons is good enough. Minos are cheap but you would need x2 battlemage and portalwalker for good alt dmg... and spirits. Fire Amp could be cheap but there are a lot of expensive things are there but it can be done as well. Imps: expensive Bok/Bleed expensive Deep Elf- cheap Demon - warrog, nefari guardian, servile brute etc. cheap You can make a budget bg but you will have to ask around for one or wait for another answer for an ideal rare-common bg.
Don't have anything to trade lawl. Gave all my runes 1.5 years ago and cameback a month ago. 30 exos and 13 legs (extended) so far.