I'm curious to hear others' input as well. I've been thinking of upgrading for a year now, but our volume is only around 1,400 booklets per month, maybe 2,000 the busiest month, and that's not been enough to really pay for an upgrade.
Right now using our MBM collator and Sprint bookletmaker standalone because of the unreliable jogging sprint interface and unacceptalbe losses using it (more loss in print costs mangled than I make in 3 hours time!), I can hand feed the 1,400 booklets in under 3 hours including the time to reload the collator. So it takes a lot of 3-hour-shifts to add up to $5000 for an upgrade... it appears I've become the collator-bookletmaker interface!
You won't find air feed collators for a limited budget - no one seems to give up the air feed towers so the price remains quite high. The need is really mainly for difficult/coated stocks... we run digital output on uncoated bond and with friction feed, 10 bins per booklet, we get about 8 to 10 mis-pulls per 1000 booklets which is acceptable. (a lot of static in play too; I do like the fact that the plockmatic/mbm collators have 4 pickup tires per bin instead of the old-model duplos which have only one pickup wheel per bin)
If you need more than 10 or 12 bins (which I wouldn't mind having for those few larger jobs), the old horizontal bourgs are really tempting because it seems the second towers for tower collators almost never go up for sale and the pairs of tower collators command a really high price used due to limited supply. Also the trimmers for a plockmatic tower setup go for around $2000/$2500 just for the trimmer. The horizontal bourgs go pretty cheap right now as a collator+stitcher+folder+trimmer, but for a 24 or 30 bin horizontal bourg, that's a lot of feet of collator taking up the floorspace here as well as we have a small space. But there are so many on the market that it's tempting... I've never run one though so maybe there is a reason that these old analog horizontal tanks are so plentiful on the market. Then again, there must be a good reason that so many were sold in the first place and bourg certaily has the reputation... I suspect the huge space they take up is a reason many are up for sale.
Look forward to hearing from other people who have more experience. Our way right now isn't elegant but it works, and 3 hours isn't bad labor, but still at some point it would be nice to automate too.