I think AvJet is a great way to go. Probably as pricy as TAG, but you'll get what you pay for. Most of the managed clients have been with the company for years and aren't planning on going anywhere else. Maintenance is excellent, the neogtiated fuel rates are incredible, and you can bet that if the plane is not on a 91 trip, they will have charter for it to fly. Training is mostly done at SimuFlite every 6 months, plus MedAir and CAPPS for all crewmembers each year. You can expect to stay within the planned budget, unless, obviously, there are some unforseen cost, ie. crewmembers leaving (with 100 hours a month flying, you may want to expect that), unforseen MX, etc. While based in KBUR, there is a reason AvJet is picking up more managed clients on the East Coast and in the Midwest - you get what you pay for, no surprises.
I do agree with the others, in that 50 hours charter/50 hours 91 is unlikely with 4 pilots, or even with more pilots. 50 hours of flying for the boss puts the plane off line for most of the month, leaving very little time for it to charter. I know every management company is going to tell you they can do it, but take that as a sales pitch and expect more in the realm of 50 hours 91/20 hours charter as a reasonable guess on the actual times.
PM me if you have more questions.
Dru