At this stage in the game Dave you cannot purchase LW 30 anymore because it too has been manufacture-discontinued but don't dispair, you can still go forward. My own guestimation is going from LW29 will cost somewhere around $5000 which will get you all the way up to the very latest load, LW33, but software only, no additional features and no hardware. What's tragic here is that procrastination probably cost you almost $2000 of that total compared to what the same upgrade would have cost last year. From what I know of your current system I think you're probably OK on hardware and most circuit cards, because I know you have an RSD drive and that requires an updated MSX card which you obviously have else your RSD wouldn't work. I'm guessing you have a 120 meg or larger hard drive. If not, that will be an additional expense. The Main control card also needs to be an MC-215AD, aka the MC-3E for LW 32 Rls 1 and above. The secondary market can probably help you there.
In considering these expenses, you probably need to be made aware that you also have the option of upgrading to a 3300-MX with a triple-fim card that will plug directly in to your MicroLight in place of your existing main controller, thus allowing you to have the advantage of the latest IP system and still be able to reuse all of your old peripheral cards, T1/PRI cards and instruments, everything but COV. Sorry I don't know cost, obviously more than $5k, but the software load on the 3300 is pretty much wide open, all options enabled, even Hotel/Motel. All you pay for going forward is IP set/user licenses and voice mail licenses if you need them. TDM licenses are all on by default. The 3300 chassis will also allow you to do tenanting, tho I believe that's one license you may need to add. (I don't think that one is turned on in the 3300 bundle).
If you're planning to keep your Mitel, the 3300 upgrade option would probably make the most sense.