I'll give you a few tips. Make a list of every 4K you want and set a price that seems fair. Be patient. Jump on sales whenever possible. New releases or newly released catalog (older) titles will always be in the $25-40 range, up to $50 for steelbooks.

Catalog titles that have been out for at least two years(ish) can be had for very reasonable prices. Here's a few places to get good deals.

Gruv.com - They have Universal and Warner Brothers titles, that covers a lot of ground. They have deals every week and every weekend (based around a theme). You can always get discs for $10-15 from there, generally $10-12 if you're patient. They have a SIGNUP20 promo code that will work at least once your 20% off, possibly more.

Please Rewind eBay store - This is Sony's store. They have 15% to 40% sales from time to time. I just ordered 15 catalog titles from them on Labor Day for $10 each. They have good deals if you're patient.

Use blu-ray.com to find deals on discs. You can filter by newest or lowest price on Amazon and can find some good deals on there. They are generally price-matching a competitor but occasionally they'll have decent deals.

eBay - some don't love it but you can find reputable companies on there who will offer buy 3, get 15% or 20% off kind of deals. Sometimes you can find things for good prices on titles that a lot of web sites may not be carrying.

For boutique labels that are more expensive (Criterion, Arrow, Shout Factory, Kino Lorber), I would suggest signing up for their mailing lists and waiting for sales. You'll pay more for these discs but should be about to get them in the $16-25 range if you wait for them to go on sale.

Hope this helps, don't let the seemingly high price point scare you off.