I think it'd be a false economy for you:
- If you could find a new LM-1 retail, you could expect to be asked to pay the retail price which would be about the same as what an LM-3S would cost.
- If you found a new one via a private seller, I expect to pay a little less than retail but not significantly so.
- If your happy with a used LM-1, then any price goes (there is a used one on eBay right now for $15.00).
As for using an LM-1, well I don't have any so I can't confirm this 100% but an LM-1 might not play nice with later LM's; plus an LM-1 most likely can not use the current lighting effects or sounds as it's internal software is too old, and no update to that software is going to be forthcoming. An LM-1 also only has 4 outputs but I imagine that is not one of your concerns.
You could try it if you could get one cheaply enough that it wouldn't matter if it didn't work out but personally I wouldn't bother and I'd just put aside what you could each week and get LM-3S's as you can afford them and try not worry about how long it might take between each LM purchase. Hard I know but sometimes that is what we must do.
We are all waiting for that magic 21 pin LM but.... well, we've all been down that road before.
- Tim