We were in the same spot last spring. I ended up leasing first, because buying a /24 felt like a big commitment while we were still figuring out growth. The IPv4 marketplace at InterLIR listed rental from around 110 euro per month for a /24, with no hidden fees and an automated LOA, so we could announce the block quickly. If you decide to buy later, they say they source from real network owners and offer escrow for bigger deals. Before signing anything, I’d check the block’s history on a few public blocklists yourself. One more thing from experience: ask how long the LOA takes after payment, because the day you pay is not the day you can announce.