Letting them drop is taking a risk, cos there are vultures like us here at dnforum, that pounce on expired domains..
That's my best explanation of dropcatching LOL vultures waiting for a feed.
P.S. Enom will "normally" give you the full 30 days after expiration to renew them. I say "normally" because I have seen some good ones go in to extended redemption after only a few days, then it will cost $160 to renew.... Take your chance..
But you have about 6 weeks to get your 100 bucks to Enom.. Not too difficult really.. Or send them a cheque, the 100 bucks is only a paypal minimum.. No minimum with cheque (check) funding option.
But if you struggle, send me a PM and I'll help you out. Domains can still be pushed within Enom whilst in an expired state.. by using the "push a list" option you can push an expired domain to another enom account.