500,000 is probably a bit more than you really spent...
If you could buy 30 runes for a page, and they cost 2,000 per rune you would spend 60k per page, and if you couldnt reuse any of the runes you could still do this 7 more times (8.3 60k rune pages).
Of course you have to buy rune pages, so probably just 7 of these 60k rune pages, but 7 pages at 60k is only 420,000 IP. You start with 3 pages as I recall, so you can buy like 12 rune pages with that... This of course assumes each rune cost 2,000 apiece.
Well one thing is clear, you dont know the exact number, but If its over 500k, I would honestly be shocked unless you were buying full rune sets of tier 1, 2, 3 runes before they lowered the price on 1/2 tier runes to 1 IP.
Not calling you a liar, just seems mathematically improbable. A realistic extreme price for a rune page + "expensive" runes to fill it with would be 29,055 IP. That would be 3 Quints @ 2,050 IP, and 9,9,9 Marks, Seals, Glyphs @ 820 IP, and one rune page @ 6,300 IP.
Last bit O' math:
500k / 29055 = 17.2
Thats 17 potential rune pages where you cant reuse any of the runes. I really am curious if you have full sets of tier 1 and 2 runes, or you have been just buying full sets of all the runes, or what. I really am curious.