right, you're in my house now 🙂
you've got options. Most venues will offer various rates based on what you require, usually including the room. They'll be the likes of dinner+B&B, Dinner only, Dinner + drinks reception etc.
if you bring in outside caterers you will have to pay corkeage on any booze and pay for the room hire.
price wise, for a decent dinner+B&B you're looking at anything from £100 up to well, anything really. Room hire only will be somewhere along the lines of £10 to £80 per person capacity but this depends massively on the hotel.
If you nook your room for a school holiday or outside the wedding season you will get a better rate.
For 150 people you will need a PA system if you plan to have after dinner speakers, a hotel will be able to supply this at a suitably marked up price. You can go direct to an AV company (like me 😉 ) for it instead if you wish.
Florists will be able to tell you about table centres etc. If it's a fund raiser i'm guessing you'll have an auction, you need someone competent to handle this or they go on forever and become a nightmare.
After dinner entertainment will depend on your audience. If it's a sausage fest then a DJ will go down like a lead balloon. In my experience (considerable) of after dinner speakers it is best to go with someone you have seen before do the same thing. Some people are great, some people are truly dire. Jimmy Carr is good and a great guy to boot but may be a little over your budget.
I'm not a fan of putting performances on over dinner, people just ignore it anyway which is horrible for the performers although a DECENT local school string quartet or similar always goes down well for a local event. 'Sexy' classical acts are all the rage at the moment, I'm not a fan but they tend to pamper to both sides of the audience, women can look at nice frocks and listen to soppy classical hits and men can…well they just dribble really.*
some things do work during dinner though, spanner in the works are brilliant and really create a buzz, as does a decent magician.
I notice you are an academic, you may be able to draw on the experience of your colleagues and AV department as well as perhaps a university venue?
If you let me know where you are I've more than likely been to or know someone that has a venue near you!
*reading that back i'm keen to point out that 'local school' and 'sexy' are entirely separate things in that paragraph 😐